This is a reasonable question, but if the API is authenticated, you may have made some agreements to get authorization to use it. Criminal prosecution could be overkill, but that’s not what is happening here.
It’s kind of like asking “what’s the point of letting me into your warehouse if you didn’t want me to take the compressor that was in there?” but you signed a contract not to take the compressor before they gave you the key to the warehouse.
It's more like: why can't I send an agent to get what I need from the warehouse instead of going myself?
I should be able to create my own user agent for a website if I want. I should be able to replace their web application and non-free javascript with my own software.
I mean they're a gussied up advertiser, of course if you mess with their "engagement" or bottom line they'll ban you. It's like the "rubber hose crypto breaker" XKCD.
If they ban me, they'd probably be doing me a favor. Actually sending people legal bullshit over this? This is some sort of legally-sanctioned bullying.
It’s kind of like asking “what’s the point of letting me into your warehouse if you didn’t want me to take the compressor that was in there?” but you signed a contract not to take the compressor before they gave you the key to the warehouse.