I know it's possible to detect incognito testing for specific APIs and browser behaviour, but it's a very brittle method as every new browser version changes so

I know it's possible to detect incognito testing for specific APIs and browser behaviour, but it's a very brittle method as every new browser version changes something here and there. Anyway I've never encountered a website doing such a thing. Perhaps I'm unknowingly blocking the gatekeeping scripts. Also why prohibit incognito browsing? Cookies?