First off, note that the limit automatically increases if the backlog gets really big. It's more or less permanently 40/day on Stack Overflow simply because thousands get added every day.
But 20 reviews per day, every day, is a lot of reviews. Very few people have that kind of stamina.
Yes, it's tempting to sit down and do 40, 50, 500/day when you're starting out. That gets really old really fast. Moderators have unlimited reviews, and yet the reviewing-est moderator I'm aware of on any site still usually did well under < 100 per day. If you're in this for the long haul, you don't want to burn out on it.
That's not even getting into issues of fatigue; even at 20, it's not uncommon to see folks getting a bit sloppy toward the end, especially if they're also active in other review queues.
If it needs to be increased for the purpose of finishing the current cleanup, we can do that, but hopefully that isn't necessary. Encourage more people to review; many hands make light work.