When a big wave election comes along usually a midterm against an unpopular incumbent president (2006, 2010, 2018, 2022 are recent examples), you always have a lot of politicians decide to not run again. They take a look at the polls, and decide it ain't worth it. Why take their re-election funds and spend it on a losing battle. They take their large re-election campaign war chests and wash the money through a non-profit and get the money back in speaking fees or being overpaid for a no show job.

Example: Paul Ryan in 2018, as Speaker of the House had a $5.8 million dollar war chest.https://www.opensecrets.org/members-of-congress/paul-ryan/summary?cid=N00004357

Ryan couldn't take the war chest as personal funds (though you used to be able to), he had to wash it first. Initially, he makes a large tax deductible donation to a non-profit with that money, which paid him a large salary. Later, he starts his own nonprofit with that money, which pays him handsomely. He uses his connections with lobbyists next. Want to get a meeting with X person still in office, pay Ryan $XXX and he can arrange it.

So, it's about them getting their money, not some "they see the covid conspiracy is going to blow wide open and they will go to prison" or some "two more weeks" type of thing.

Lastly, there are only about 30-40 "swing districts" in the House. These are non-gerrymandered districts where there is no inner city County Clerk cheating on the behalf of the democrats. Typically, this is suburbia somewhere. Most everybody is in a safe seat, so you're not going to have more than 30-40 members of the House go from Dem to GOP.