There wasn’t much of a computer game industry [in Japan] because almost everything was arcades and consoles, so to be able to write game music you had to have a devkit, which cost thousands, and a development license, which was nigh on impossible to get if you weren’t an actual company.
Therefore, to create music, you had to first get a job at a game company [in Japan]. Unlike in Europe, you couldn’t write your own play routine at home. The barrier to entry was way too high. The few actual programmer/musicians like Yuzo Koshiro really stood out.
The Americans have this weird fetish about Japanese game music on the home consoles when in reality it wasn’t really very good. There’s not really anything particularly impressive until the Mega Drive and even then, there are only a few standouts like Streets of Rage and Sonic.