I’ve been a DM for many years, and in all that time I’ve had maybe three players read the PHB. I don’t mind explaining the rules, but it would be nice to not have to remind the wizard how spell slots work (again). Is this a common thing for most groups?
Depends on the casualness of the group.
Pick-up games, almost nobody knows the rules. Don’t use complex games with them, use tiny little indie games instead. Get an OSR game like Knave, and it’s almost impossible to not understand the game.
Longer-term groups, I do expect everyone to read the rules, and using more complex games is fine. Someone who won’t, and especially if they picked a more complex class or skills, needs to read the book, change characters, or go to another group.