That doesn't really matter for a company that has already raised some money and now desperately looking to get out of red, does it? (I'm not talking about Reddit or any companies in particular right now, just remembering my mind state when I was CEO/Founder: I can almost feel that desperate depression again).
Indeed this matters a lot and is what is called "business model". Just to give a comparison:
a) Users are willing to give away some of their personal data. Unluckily it seems not to be easy (for various reasons that are off topic here) to monetize this asset for many companies so that they can't or have difficulties to use it to get out of the red.
b) Users are willing to give away their money. As I've shown this asset is also not that easy to leverage, thus also not easy to use to get out of the red.
Perhaps there are other reasons than not willing to. Say, for example, in Germany credit cards are not that common (other methods, like SEPA direct debit are used). Or they are in principle willing to pay, but not for the product that is offered (say, because of DRM or watermarks). Or they would pay, but don't trust their credit card number to some small, dubious website. Or they would pay, but are afraid of some hidden usage terms for the website that implies some kind of subscription (and thus future payments) that you don't want.
TLDR: There are lots of other reasons that can explain, why people would love to pay, but don't.