They collect stamps because the hobby brings them joy and satisfaction. Even if they are mocked by others who don't understand how they could enjoy such a thing.
It is not necessary to attribute to ulterior motives to what can be explained simply by different interests.
I'm sure there are aging collectors who mistakenly think they are leaving a stamp collection that could be of financial value to their children, but it is likely that they also have the wistful albeit unlikely hope that someone of the next generation might take up the hobby that has given them pleasure.
And if there haven't been collectible pumpers in your hobby before (a doubtful claim), it's all the more attractive for them to be the first.
It's not technically a Ponzi scheme since (from what I've seen) the comics are (at least nominally) presented as something you would want to own for the sake of owning them, rather than solely as a investment vehicle. Compare houses, which exist for the purpose of living in, while property appreciation is (supposed to be) at best a nice side effect. (Although unlike housing, there's no strong reason to apply felony penalties to using comic books as a investment vehicle.)
I've seen this exact same discussion on comic book boards that I frequent, where some collectors worry that Golden Age and Silver Age comics may drop in value because they don't have as much meaning to newer collectors, who buy Modern comics for different entirely reasons. It's kind of a funny discussion to me, since they are literally trying to keep a Ponzi scheme going at the expense of younger people and new collectors.