“members of the president’s party often leave Capitol Hill during a midterm cycle because they expect the next election to go poorly. The president’s party almost always loses House seats in midterm elections, and the more unpopular presidents are, the more ground their party tends to lose in the House. Considering President Biden’s approval rating sits in the low 40s less than 10 months before the election, 2022 could sting particularly badly for Democrats.
It’s no surprise then that more than twice as many Democrats as Republicans, 28 to 13, have decided to either retire or run for another office at this point.”
https://fivethirtyeight.com/features/why-28-house-democrats-arent-running-again/