Many of the games were ported from the Arcade systems. Since the Arcade systems were all using limited color space to begin with, that is what you got with games.
SEGA on the other hand, was moving towards the future, while the PCE was just made to imitate animation data. The SEGA-CD is basically a pre-DVD game machine. The PCE outlasted the Sega Saturn, only after the N64 came about PCE was on the short end of the stick.
That is probably why SEGA decided to favor NEC, because everybody knew the saw it as a second PCE, even if it was censored as hell. This could also explain Hudson Soft, and red making so many Saturn titles.
This brings us back, why didn't SEGA just implemented support for the Hu-cards on the Saturn. Another swing and miss.