[TMWNN]

>I had a C128 as a kid, but I almost exclusively booted into C64 mode to play games.

95% of C128s spent 95% of their time in C64 mode.

>I did have a CP/M floppy, but I only booted it once or twice, had no clue what to do with it, and forgot about it quickly.

If 1% of C128 users ever used the bundled CP/M disk for more than what you did—boot it to see what it's like—I'd be surprised. 1985 was just too late to expect people to buy a new computer to run CP/M.