Despite its obviously far lower MIPS rating the 6502 could just get more "video game" type work done in a clock cycle than a 68000. 68000 interrupt responsiveness was also pretty terrible.

Looking back 68000 had little business in video game type machines. I like the 68000 from a programming POV but it's faster for doing a pile of fast integer calculations than it is at moving memory around and responding to interrupts.

But Atari and Commodore were also imagining their machines to be targeting productivity more than games, so.