Whether a website offers a useful API depends, in part, on whether its owner reacts to automated use of the site with encouragement, indifference, or hostility.

Whether a website offers a useful API depends, in part, on whether its owner reacts to automated use of the site with encouragement, indifference, or hostility. API's are offered by sites that either (a) actively encourage automated usage, or (b) are indifferent to users' use of their API, but provide it to users because it's easier to develop their own pages' JS that way. Robot-style automation is a sort of "backdoor" that allows automated interaction with any website, no matter how hostile its owner is. You can't do much about automation that pretends to be a human. (Except maybe deploy a CAPTCHA, but solving a CAPTCHA is an annoyance users generally won't put up with more than once per login. And your RPA could simply defer to a human to login and solve the CAPTCHA, then take over for the automation part.) In some domains, a competitor that offers an automated interface to the same data will outcompete a site that doesn't. But in other domains, you can't start that competitor, because the data to back the API isn't open. For example, if we lived in a world where say Facebook provided only pre-rendered pages and had no API, you couldn't make an API to allow automated access to Facebook data. If you made a Facebook clone with all the functions of Facebook plus an API, it still wouldn't be the same site as Facebook plus an API -- the users and network effect would still all be on Facebook. Your clone would likely never be able to outcompete Facebook.