Simple: boredom.
If you can only swing having up to a few games, it is understandable if they get boring.
If you have a large collection and you bail, you probably never were any good at playing!
Posers with large rooms full of immaculate games that rarely get played are like rich dorks who buy original Rembrandts and Picassos and hide them away. Glory hoarders. (Although art can make pinball's market appreciation look like peanuts!)
I can confidently say that pinball will never get old for me. I just hope I never get too old for pinball!