Well, let's put it differently: all those hypothetical services are using the API in question, so your marginal cost for them taken together adds to $20/month, which they'll pass onto you, and you'll then happily pay, because you find the services useful.
Maybe. I’m pretty frugal and a big fan of doing things myself. I certainly hope that they can some day can provide me with enough value to make spending $20 a no-brainer, but until that’s obvious or unavoidable, I’m not giving them $20 ¯\_(ツ)_/¯
