I agree with you wholeheartedly that it should be fair game, but ultimately, if reverse engineered users are creating, say, 50% of traffic[0], because they're polling instead of using the proper push mechanism, these sorts of companies can and will get upset.
Frankly, as a backend software engineer myself, if any system I built with the purpose of being constantly accessed by a fleet of devices sold on the open market couldn't handle the relatively tiny numbers MyQ created a fuss[1] over, I'd be embarrassed.
[0] https://chamberlaingroup.com/press/a-message-about-our-decis... [1] https://www.home-assistant.io/blog/2023/11/06/removal-of-myq...