Based on the movie Stalin (1992) from HBO (You can watch on youtube), Stalin volunteered to take General Secretary because Trotsky, Kamenev, and Zinoviev did not want the position. Stalin was recommended the position because those 3 that I mentioned above wanted Stalin out. They thought by giving Stalin a position, it would keep him busy from matters with Lenin. But they were sadly mistaken later on in the power struggl of the 20s and purge of 1936. Stalin was choosen to be GS because everyone knew Stalin's ability to memorize and organize. So they thought his position was meaningless and simple.

Stalin proved himself competent to Lenin when he was People's Commissar for Nationalities (this position was integrating ethic groups in different countries such as Kazakhstan, Armenia, e.t.c. into Russia). Stalin had excellent organizational skills, and Lenin saw that and promoted him to a higher position. Lenin did not know that Stalin was smart in a way that he would misuse the position of General Secretary.

The circumstances of the initial appointment in 1922 are debated, but Trotsky claims that Lenin was opposed to it and only reluctantly agreed - saying about Stalin that "this cook will only prepare peppery [in Russian: sharp/spicy] dishes". Nobody besides Trotsky has directly confirmed this statement, but it became well known and other Bolsheviks opposed to Stalin quoted it later. When the issue of his excessive power over the Secretariat becoming power over the party (since he selected regional secretaries, and half the CC in 1924 was composed of the regional secretaries, mostly indebted to Stalin's Secretariat for their jobs), Stalin did offer to resign the post (obviously as a symbolic gesture) and his colleagues (especially Zinoviev and Kamenev who were still allied with Stalin against Trotsky) "pressured" him to stay.

In one of these instances after Lenin's "testament" erupted into an intra-party scandal (the "testament" was just a dictation of the ailing Lenin calling for the removal of Stalin from the post of General Secretary among other things), Stalin said: "At the very first plenary meeting of the Central Committee after the Thirteenth Congress, I [Stalin] requested the Central Committee plenum to release me from the duties of general secretary. The congress itself discussed this question. Each delegation discussed this question, and all the delegations, including Trotsky, Kamenev, and Zinoviev, obliged Stalin to remain at his post. What, then, could I do? Flee the post? That is not in my character." (this was quoted in Pravda of 1927, and in Tucker's biography of Stalin, Vol 1)

It was considered a menial position wasted on Lenin himself, Trotsky, or Zinoviev

It's not completely accurate to say that the General Secretary was created in 1922. The position evolved out of Technical Secretary of the Central Committee, which then became the Chairman of the Secretariat as the administrative needs of the Bolsheviks evolved. Then it became Responsible Secretary, and finally General Secretary.

At its creation, the post was a purely administrative one, like the Secretaries before it. Lenin even referred to Stalin as "comrade card-index." However, one of the things it controlled was the membership of the Communist Party. Stalin took advantage of this as a way to build up a power base in the Party and reduce the influence of his enemies.

The General Secretary post became influential because Stalin was influential, not the other way around. Originally, the Chairman of the People's Commissars (Lenin's position) was the leader of the nation.