It's borderline inexplicable to me. How could someone want this in the first place and how could they be willing to do it in a volunteer capacity?
Sure, the major frontpage subs will be fine, but there's plenty of more niche communities that are already dying/getting banned for being unmodded because no one wants to mod them. I literally opened a link to a sub today that was banned for being unmodded 2 hours ago, presumably because the last remaining mod deleted their account.
So many of the discussions here seem to be people mostly thinking of reddit as the big frontpage subs, which also seems to be what Reddit Corporate seems to think. What we're all likely about to see is how much value there is in the longer tail of smaller subs that are being run as a passion project by a few people in a niche community. It's easy to point to the small subs that are some power-trip for one mod or set of mods, but there's also plenty of small little subs that are niche and interesting and simply would never have enough interest or activity to support more than 2-3 mods.
I wasn't sure what it was going to be like when I was invited. It's not fun telling people to behave, but I've found a lot of personal satisfaction in coding moderation tasks and working with the team. There are whole classes of work that I've automated away and it's easy to deploy improvements.
There's also plenty of people who like the authority, or a thousand other reasons, but that's one example.
Being a gatekeeper for a popular subreddit is a form of meaningful influence. Meaningful influence can lead to money and other benefits. Reddit mods in the past have been exposed for using their influence to push certain content and block other kind.
Remember, "Most of What You Read on the Internet is Written by Insane People". <https://np.reddit.com/r/slatestarcodex/comments/9rvroo/most_...>. This also applies to powermods, assuming they're not being paid on the side to push some ideology.