Doesn't seem especially out of the norm for a large conference. Call it 10,000 attendees which is large but not huge. Sure; not everyone attending puts in a session proposal. But others put multiple. And many submit but, if not accepted don't attend.
Can't quote exact numbers but when I was on the conference committee for a maybe high four figures attendance conference, we certainly had many thousands of submissions.
The problem isn't only papers it's that the world of academic computer science coalesced around conference submissions instead of journal submissions. This isn't new and was an issue 30 years ago when I was in grad school. It makes the work of conference organizes the little block holding up the entire system.
