Businesses are almost always built on top of someone else. What you need to make sure of is that your financial interests are aligned.

Which is to say have a contract that your counterparty can’t redefine freely.

Was there a contract or SLA for the free Reddit API?

If not, then there isn't much to complain about

The terms of service are the default contract. Presumably it has a we-can-screw-you-whenever clause, but sometimes the corporate lawyers screw up and you can actually get them for violating their own ToS.

Build your own rug before the rug pull comes.

Its rugs all the way down!

Indeed, Courtland, and even on IndieHackers you see a lot of stories about platform risk, platforms which indie hackers often use to build a good product but always seem surprised that they got rugged, as if the previous X stories didn't show that it inevitably happens.