Most likely anti-scraping measure. So they can detect and shut down bots or really anyone they feel like if activity looks nonstandard. Not suggesting it’s good, but it’s consistent with the in vogue trend to lock down recipient public APIs nowadays.
As an illustration, near the end of last year, bots from a renowned Email API provider spotted in less than 1 hour the leak of a public key from my public GitHub code repo. My account got suspended on their platform. It was stunning to see the speed at which they acted and automated the process to "lose" and "recover" reputation.
