This is it in a nutshell, without any "late stage capitalism" nonsense.
Reddit, like Twitter and other prominent tech companies, was supported largely by outside investment. The company didn't make a profit, but investors continued to put money into it in hopes that it would eventually net them a return. Low interest rates make investment capital easy to come by and relatively low risk, but higher borrowing rates have dried up a lot of that funding. This forces the company to find other ways of sustaining itself.
I have like three now, because it wasn't clear that that wasn't required. I think I'm getting it more now, but it's taking a bit to get there.