Glicko ratings on the site

I just noticed that the average ratings on the site have plummeted from what they used to be.

A couple of years ago, Chess.com claimed the average rating was something over 1000, but now, when I looked at my ratings, blitz and rapid ratings are about 800.

This does not make intuitive sense to me. If players start at 1200 and then swap points with their opponents depending on results, shouldn't the average stay close to 1200?

If people leave the playing pool and take their points with them there could be a loss of points in the pool, but I would expect mainly weaker players would give up playing after losing too many games, so the average rating should rise as the departing players leave the points that they have lost in the pool which is now smaller.

Can somebody with some level of statistical calculation expertise explain why the average has deviated so far from the old value and from the starting point for new players?

New players haven't started at 1200 for years.  Currently, they are asked to self-assess and are started at 400 for players new to chess. Other start at 800 to 2000.