the command /maxlives does not update the game instantly like /maxscore. You have to restart the level for the /maxlives to trim players maxlives to the given amount. I know /setlives <player> <lives> exist, but logically cutting /maxlives from 5 to 1 should not make it possible to still have 5 lives.

Can this autotrim feature be given to /maxlives?

I don't know how trivial this would be without looking at the code--or what BlurredD's motivation was for designing it this way, so there may be something we're not thinking about--but in passing, you can use /reset for this, you don't need to use /r.