With the more powerful systems comes more realistic depictions of violence, blood, and gore, that's why something like Jet Force Gemini could get away with a T rating back then but not now.
If there is any blood splatter, that game is going to get an M rating. Goldeneye got a T rating because when you shot somebody, there would just be a red spot where you hit them, no splatter. In Perfect Dark, blood could end up on walls or pool under bodies, so it got an M rating.