^{PzKpfw V "Panther" Tank 1944. Source: Wikipedia}

Short Answer

As Samuel Russel pointed out, the Panzer Mark V was a complex and unreliable platform, requiring serious support logistics. This made it less desirable.

And there is second factor to consider — availability. Post-WWII there were not as many surviving / serviceable Panthers as there were PzKpfw IV tanks.

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Long Answer

1. Serviceability / Reliability

Here are some indications of the complexities involved in supporting Panthers in the field, from German perspectives as well as from other capturing forces.

The Germans had to develop a new recovery vehicle, the Bergepanther based on the Panther Ausf.D platform, to support recovery of the heavy Panthers and Tigers in the field:

The idea of ​​a Bergepanthers was created in 1943 because of problems with the recovery of heavy and medium-heavy tanks. ... The half-track vehicles previously used for recovery (eg Sd.Kfz. 9) were seldom able to successfully salvage a Panther or a Tiger; Towing with another Tiger or Panther was strictly prohibited as it could result in the loss of both tanks.

^{Source: Wikipedia}

The Soviets captured some Panthers during the war but found them hard to support:

During the war, the Red Army employed a number of captured Panthers. ... Unlike captured Panzer IVs and StuGs, the Soviets generally only used Panthers and Tigers that had been captured intact and used them until they broke down, as they were too complex and difficult to transport for repair. Panzer IVs and StuGs, on the other hand, were so numerous in terms of spare parts and easy to repair that they could be used over a much longer period in combat conditions.

^{Source: Wikipedia}

Also, Tank and AFV News has an interesting article on Panther Reliability which is compiled from several books inlcuding Germany's Panther Tank by Thomas Jentz, Panther: Germany’s Quest for Combat Dominance by Michael and Gladys Green, Panther and its Variants by Walther Speilberger, Panzers at War by Michael and Gladys Green, Panther vs T-34: Ukraine 1943 by Robert Forczyk, and Panther vs Sherman: Battle of the Bulge 1944 by Steven Zaloga.

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2. Availability

The number of Panther tanks available for serviceable use after WWII didn't add up to a large number [Source for below: Wikipedia]:

During March–April 1945, Bulgaria received 15 Panthers of various makes (D, A, and G variants) from captured and overhauled Soviet stocks; they only saw limited (training) service use. They were dug down, with automotive components removed, as pillboxes along the Bulgarian-Turkish border as early as the late 1940s. The final fate of these pillbox Panthers is unknown, but sources indicate that they were replaced and scrapped in the 1950s.

In May 1946, Romania received 13 Panther tanks from the USSR. They were initially used by the 1st Armoured Brigade, but in 1947 the equipment was ceded to the Soviet-organized "Tudor Vladimirescu Division", which was transformed from a volunteer infantry division into an armoured one. The Panther tank was officially known as T-V (T-5) in the army inventory. These tanks were in poor condition and remained in service until about 1950, by which time the Romanian Army had received T-34-85 tanks. All of the tanks were scrapped by 1954.

In 1946, Sweden sent a delegation to France to examine surviving specimens of German military vehicles. During their visit, the delegates found a few surviving Panthers and had one shipped to Sweden for further testing and evaluation, which continued until 1961.

After the war, France was able to recover enough operable vehicles and components to equip the French Army's 503e Régiment de Chars de Combat with a force of 50 Panthers from 1944 to 1947, in the 501st and 503rd Tank Regiments.

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Syrian WWII Armor

There is not much reliable information on the fate of the bulk of the post-WWII surviving Panthers beyond ~1947-1950 other than the few museum and collectors' pieces here and there. So what did the market look like for Syria among their principle weapons sources, France, Czechoslovakia and Spain? Panzer IV's with all their spare parts and less complexity, were still available. This below is from Wikipedia's Panzer IV article:

While their numbers remain uncertain, Syria received around 60 [Panzer IVs] that were refurbished in France during 1950-1952, followed by 50 others purchased from Czechoslovakia in 1954. A Soviet DShK machine gun on an anti-aircraft mount was retrofitted on the cupola. These were used to shell Israeli settlements below the Golan Heights, and were fired upon in 1965 during the Water War by Israeli Centurion tanks. Syria received 17 Panzer IVs from Spain; these saw combat during the Six-Day War in 1967.

Thus we see there does not appear to have been an appreciable amount of surviving Panthers available for Syria's use. However, as found in the source cited in the Question, in addition to the Panzer IV's from France, Czechoslovakia and Spain, Syria also acquired:

• StuGIIIs: nine from France, twelve from the Czechs, six from Spain and one from Romania;
• Jagdpanzer IVs: six from France;
• Hummels: five from France.

^{Source: WWII after WWII: Panzers in the Golan Heights}