What was the reason for Soviet troops to withdraw from Yugoslavia in World War II?

It has nothing to do with percentages, but with agreement between Yugoslavian communists and Soviet communists.

Tito was in contact with Comiterna throughout the war and when Soviets came to Yugoslavia. That was in fact the only allied territory, unlike all others who fought against them in one way or another. British absolutely didnt have a say in post war Yugoslavia. We can see evidence from Churchill's change of attitude towards Tito and Trieste crisis.

Even before the war was officially over, there was an incident where British sailors and SAS were trying to interfere with Partisan advance through Istrian peninsula. Partisans arrested them and immediately all aid was suspended. Tito didnt forget that both Soviet, GB and USA supported the official Yugoslavian government in exile (Soviets politically, GB and USA politically and materially). Soviets really didn't have to leave any troops in Yugoslavia since it was allied in true sense of the word. In any event both east and west were played by Tito who actually successfully established Yugoslavian national liberation movement without any help from outside. And because they did it by themselves they owed nothing to anyone.

Question:
What was the reason for Soviet troops to withdraw from Yugoslavia in World War II?

Short Answer:
Unlike most of Eastern Europe, Yugoslavia had a significant army which gave it the option of independence after the war. It's true though that because the Yugoslav Communists were close allies of the Soviet Union with their ideology branching off the Soviets; there was no reason to impose a Soviet Style Communist regime during the war because that was Marshal Tito's plan from the beginning. Stalin and Tito fell out after the war when Stalin tried to dictate to Tito in 1948. Mostly on Foreign policy.

Detailed Answer:
The Soviet Union really did not Liberate Yugoslavia during WWII. Yugoslavia was largely liberated by its own forces. Yes the Soviet's did aid Yugoslavia at the end of 44. However; The Yugoslavs had been fighting for 3 years at that point and had their own sizable military independent from Soviets. Given this there was no need for the Soviets to install a pro Soviet Communist regime in Yugoslavia. Yugoslavia was doing that themselves. So their was no reason for the Soviet's to leave troops in Yugoslavia. By the end of WWII there were no foreign troops in Yugoslavia. There was no need.

Yugoslav Partisans
SFR Yugoslavia was one of only two European countries that were largely liberated by its own forces during World War II. It received significant assistance from the Soviet Union during the liberation of Serbia, and substantial assistance from the Balkan Air Force from mid-1944, but only limited assistance, mainly from the British, prior to 1944. At the end of the war no foreign troops were stationed on its soil. Partly as a result, the country found itself halfway between the two camps at the onset of the Cold War.

When Stalin tried to dictate Yugoslavia's foreign policy after WWII, in 1948, that's when Stalin and Tito had a falling out. Yugoslavia did not join the Warsaw Pact and in 1948 Tito blocked Russia from supporting a Greek Revolution siding with the West. (the Greek red army collapsed when Tito refused to permit Stalin to resupply them through Yugoslavian territory). Tito also broke with the Soviet Union over the Marshal Plan. Yugoslavia was the only communist country which participated in it. Throughout the cold war Yugoslavia benefited from aid from both the Soviet Union and West.

During the cold war Turkey and Yugoslavia had a mutual defense pact. Yugoslavia had no such defense treaty with the Soviet Union; Which basically made Yugoslavia loosely associated with NATO rather than the Soviet Union.

Tito was a master of deception. After finally meeting Churchill in 1943 and getting his support changed from Draza Mihailovic's Chetniks to his communist partisans, Tito flew to Moscow in 1944 to obtain the Soviets' support for the liberation of Belgrade. Tito had one condition for the Soviet troops - not to use heavy artillery during the liberation of Belgrade.

As a consequence, the Soviets had heavy casualties during the street-to-street fighting with retreating Nazi troops. Once when Belgrade was liberated, the Soviets installed heavy artillery on the banks of Danube from which they started shelling of Zemun, the Croatian city ruled by the pro-Nazi Croatian Ustaše. The Russian statement of proclaiming Croatia an easy campaign led to the complete devastation of Zemun. In order to preserve the rest of Croatia from Soviet shelling Tito thanked Soviets for their help and asked them to leave the liberation of Croatia to his partisans troops.

The Soviets only had a small presence in Yugoslavia, during the capture of Belgrade where they only had an assisting role - Tito's Partisans proved more than capable of defeating the Nazis on their own. The troops in Yugoslavia, the 2nd and 3rd Ukranian Front, were needed elsewhere, and so were redeployed to Hungary once it was clear the Yugoslavians had things well in hand.

The Wiki article on the Tito-Stalin split has some more background on how Yugoslavia avoided becoming a satellite state of the Soviet Union.

There were a couple reasons. The first was that Tito basically represented "a government of their [Soviet] choice". The second was that Tito showed that he could "take care of himself".

Josip Broz Tito had started with the Russian Communist Party as early as 1917. When "Russia" became the Soviet Union, he was a member of the Soviet Communist party and secret police, before he went back to Yugoslavia. He was highly regarded among Soviet and East European Party members. Essentially, Stalin couldn't find a "better" Communist.

The other reason is that Tito had led the resistance movement beginning in 1941, right from the beginning of the German occupation. He even established a short-lived "Republic" later that year. Given that he was able to keep part of Yugoslavia "independent" of the Axis, he could do the same, if necessary, vis-a-vis Stalin, who preferred to have Tito "nominally" under his control, than an open enemy.

The Soviet troops withdrew from Yugoslavia late in 1944, en route to fighting German and Hungarian enemies, and after securing some (logistical) support from Tito.