[wmgries]

A different version of this argument is: why should it matter if I'm querying the content using the API directly versus by using the HTML web interface? If it's the case that different consumers of the API might put different load on the system than the web page that the provider can't/doesn't want to support, why isn't rate limiting the solution?

This also provides providers a way to fairly monetize their API: we're giving you some basic level of access that matches what you get through the website for free, but if your access pattern is such that you put a load on our system that we can't tolerate, then we'll charge you (by providing a paid tier).

[zokier]

The HTML interface has ads baked in, which pay for the request. API does not.