I don't remember the same happening in 4E and 5E.
In 4E I saw it a tiny bit, with the power source books, but we stopped buying books almost entirely before long because we were subbed to the DDI once it became available. That probably wasn't the greatest for WotC's profits lol, but more than one sub was dumb because they weren't linked so you need all the characters in one place on the DDI, so we all shared a logon - I think with the character creator weirdly maybe only one person could be on at once and we had to organise, but certainly with the rules encylopedia thing we could all be in it at the same time. Beyond cracked that at least, giving everyone separate and connect-able accounts, with shared content if the DM allows it (and has a paid sub - fair enough honestly).
With 5E we didn't see it at all for two reasons:
1) The books came out extremely slowly, and of them which were vital, I just got more or less immediately, as it wasn't like I was being firehose'd with books like 3E lol.
2) The books I didn't get often did have some player options (races, subclasses), but they weren't really attractive to players because the amount of options were soooooooooooooooo small compared to what was in the book generally. Like, I could easily see a player buying a book with 15+ races and 20+ subclasses or whatever, but instead they've gone up usually with low single digit numbers of either.
That's not a criticism, per se, it was an intentional and conscious strategy, and I have no doubt it was more efficient in the sense that, if you're selling printed books, you're going to sell more copies if every one seems special and important than if you firehose them. But as we increasingly go to digital...