Storage capacity isn't really an issue here, unless the NES requires a lot more data/storage by comparison for its music. Your average title track SID would occupy 4-6k in total, so not a huge footprint in the overall memory structure for a single load game.

Almost all the best SID composers came from Europe. I'm not sure why we took to it, and certainly here in the UK is arguably where SID music took off, with the likes of Hubbard (THE first notable composer), Galway, Daglish, Whittaker, Frey and Matt Grey... which led to composers such as Huelsbeck, Maniacs of Noise, and Ouwehand et al also becoming well known. It might be due to electronic music in general becoming prominent around the time the C64 launched, and the rise of one genre led to people wanting to emulate it on their own home machines.