If the company whose api you're selling, goes out of business or changes their service to no longer off the service, can you carry on doing business?

What if they keep offering the service but at 10x the price?

for reference i would say the same about more generic things like app servers, databases, email processors. The moment you rely on a vendor specific thing, you have a dependency on them. Some are unavoidable, and/or low risk. Some are avoidable and/or high risk.