It was a political decision by King Stephen I. During his father’s, Prince Géza’s reign there were both catholic and orthodox missions sent to convert the Hungarians and also both types of monasteries were being built. Most of the population was still pagan and had to be converted by force during Stephen’s reign and even later on. Stephen himself was christened a Roman Catholic (same as his father - he, Geza chose that), while Stephen’s relative and later rival in succession (which really came down to a question of western primogeniture vs a pagan-type seniorate) Koppány, was christened according to Byzantine rites. Due to his German wife (obviously a political match arranged by Géza), there were a lot of western knights (giving a lot of military support) and influence in Stephen’s court so while founding his kingdom, he mainly had western examples. He wanted an independent Hungary free from Byzantine political pressure which would have probably came with their rites (but really also from the HRE - so founding an independent ecclesial structure was important).

But even before Stephen, Géza (he tried to be on friendly terms with all neighbours to focus on internal problems/stabilisation while maintaining independence) really oriented more towards the west/Rome and lay the foundation to his son’ s success in integrating Hungary in Europe.

This is actually a very important cornerstone of Hungarian cultural thought, of the country belonging (or at least striving to belong) “to the west” since the beginning, because of this. It was a deliberate decision by Stephen I, one he had to make, given the country’s geopolitical place. [And no it had nothing to do with Romance-speaking population - there weren’t many left anyway and they were politically nonexistent. Actually (western) romance speaking people (merchant immigrants) mainly started to appear later on, when the kingdom was stabilized as a Christian country.]

Sorry for formatting, on mobile.