My impression is rather that a large part of the pinball machines which are in home collections now would be otherwise rotting on some junkyard.
There is no substantial youth market for pinball, the target group for pinball is a mix of 35+ guys reliving their youth at home or in barcades, some younger hipsters that think retro is cool (a trend which will pass) and random people that just throw money in anything that resembles their favorite theme. The last group doesn't care if it's a pinball machine or a video arcade game, if it's e.g. "Lord of the Rings" they will play it.

Actually what made me love pinball back in the day was WMS Indy. Just because I loved the artwork & music and the dogfight sounds when hitting the ramps. I could not have cared less about any rules, balltimes or whatever else, just whacking the ball around, trying to hit ramps or start multiball was enough - it was INDIANA JONES after all!

Bottom line is, noone is keeping the machines from the crowds, us "hoarders" are the only ones that care about these silly oldschool machines at all. Without the collectors the industry would be dead and buried since a long time.