Maybe it has something to do with the fact that most games now are license-oriented, so they have to use the music that goes with the film/band/cartoon, whatever, and it's limiting, in a way?
Just spitballing here, but maybe when they were creating Tales of the Arabian Nights or Attack from Mars, with a blank canvas, and they had to create it all from scratch, they were more "in tune" with the game/theme -