My guess is that a large number of younger people use the "new" reddit, and basically pay to keep everything running with the ads they view. Many older Reddit users just go to old.reddit.com, and would sooner leave the site than use the current design.

It's absolutely fascinating that they have both versions. To me it illustrates so perfectly what the Internet was vs. what is has become. There's probably more money to be made from the infinite scrolling and dark patterns, but it's also completely unusable and comments and discussions seems to be of less concern. Just keep scrolling.