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?
When I bring in a new board game I also teach it to the group. I fully expect that as a DM it is similarly a part of my responsibilities to coach the players about these rules. After all I want to play this with them.
At some point though, I indeed expect my players to have the initiative to look some things up for themselves. But the D&D PHB is 320 friggin pages. That’s not a casual “give it a quick read before our next session” kind of thing.
But I think it also depends on your schedule. We occasionally had a month or more between sessions and it’s quite natural to forget some aspects of a game (any game really) when you’ve been off for that long.