Can't compare to any hobby that can be stored in a hall closet or shoe box - baseball cards, pez dispensers, comic and can be cranked out cheaply or even counterfeited.

Pinball machines are inherently produced in low quantities, are costly to store/move, require maintenance/repair and were not originally produced for the collector market.

Pinball machines will always hold some of their value as the product provides entertainment, ability to earn money, and is truly in short supply while the value of many mass produced "collectibles" can see their value drop to zero. A baseball card is a piece of printed cardboard.