Why do you only get on extea man to work with on ms pacman?

I play ms pacman on my sons Nintendo Gameboy SP, and throughout the entire game I only recieve one extra man. That extra man comes at 10,000 points. I've gotten past 50'000 points and still, I've never recieved an extra man. It's not like that on Sega Genisis. Is there an answer out there.