Why did many commodore 64 games feature different music than their original Arcade or other computers version? [closed]

The most notable example I can think of right now are Ghosts 'n goblins and Ghouls 'n ghosts.

Converting a game from a platform to another required a license to do so, of course, so I don't think they couldn't license the same music in the same way they licensed the game porting.

I also don't think that when porting to a more restricted platform like from Arcades to Commodore 64, there were technical limitations to what music could be performed. At least the music quality wouldn't be the same, but why change it completely?

In a interview with Mark Cooksey (the one that did Ghosts and Goblins music) :

A lot of the games were arcade conversions or licensed titles and hence the music was copied from the original source, when an original product was produced the programmer would often want some of their favorite music in the game [...]

Also, note than it may not be the "technical limitations to what music could be performed", it may be some other technical limitations, like memory. In the case of Ghosts 'n goblins Elite - which had given the job for the conversion to Chris Butler - insisted on the precondition, that the game should be completely in the memory without having to reload from a media.

So I guess it was a decision that was taken over a counter-top, the only way to be sure could be to track-down and ask someone like Mark Cooksey or Chris Butler.