I've been slowly selling off for years. First, it was selling yard sale finds to fund my collection. Then, it was selling off some when I got divorced. Now, I'm in my 40s, I know I won't ever play everything I have, and I'm not a completist or too compulsive.
Now, I sell stuff that I either finally got to playing and don't like, is available digitally on multiple sources, or has gotten too expensive to keep around, due both to either maintenance (like arcade PCBs that can get corrosion) or simply so expensive that it's becoming a risk to keep them in the house.
Note also that my game collection is uninsurable and not covered by home owners insurance, so there's a small but real risk that I could simply lose everything anyway due to fire or theft. Insurance companies won't cover collectibles here in Canada, so IF I had proof they'd accept of every item I had, they'd pay a flat rate of like $15 a game. When you start having stacks of items worth hundreds or thousands that you don't use and can't replace cheaply, that's actually an issue.