I wasn't going to say anything about it because it seemed well explained enough by others, but...
I can't keep up with the 5th edition release schedule either.
I've been playing as much D&D as my group can stand to (averages out to about 2 sessions per week, though not of the same campaign) since the Starter Set came out, but we've barely scratched the surface it seems:
- None of my players have played every class they want to try out yet.
- I haven't used all the monsters I want to from the Monster Manual, and Volo's Guide is around the corner giving me even more of them.
- One campaign started with Hoard of the Dragon Queen the week it came out and hasn't finished yet, plus the campaign we started with Lost Mine of Phandelver is still going, and my home-brew campaign on top of that
- I haven't even bought Curse of Strahd or Storm King's Thunder yet because I've already got Princes of the Apocalypse on the shelf waiting to be started
And that's not even counting the side campaigns I run whenever players in the normally schedule campaigns can't show up or a few people have an extra day they can squeeze in a session, or any of the 3rd-party or DM's Guild stuff that interests me.
So just because the schedule is slower than prior editions, or because you don't personally like or "count" whatever is on the schedule, doesn't mean that people saying they can't keep up with it shouldn't be taken seriously.