Pac-Man Atari 2600 PAL © 1981 Atari

Considering the game runs in less than 128 bytes of RAM and sits in 4 kBs of ROM it plays very well. I've seen much worse Pac-Man clones on ZX Spectrum. The big complaint is the flickering of the sprites. Games like Lock 'n' Chase clearly show that you can have a perfectly working Pac-Man game without any sort of flicker even without putting extra hardware into the cartridge. Alternating sprites to increase their number? No, that is not the way to go and this obviously does not apply only to Pac-Man or even Atari 2600...

[@kotowate]

Maybe it was done to make them appear translucent?

[@wolverine9632]

It was done that way because Atari didn't want to fork out enough cash to do it properly, although even then, flicker would still happen sometimes (look at the homebrew called "Pac-Man 8K") And since the monsters looked ghostly when they flickered, they decided to call them ghosts. (I think I heard that they were never officially called ghosts before the Atari 2600 game.)