I agree with that too, and admitted to such in my previous comment. Still, being the first practitioner of this comes with a certain responsibility for its proliferation. It's not a sole responsibility to your point, but it is primary in a way. It's a lot easier for others to decide to copy what someone else did than to decide to be the first to do it.

To the same point, Google is arguably the reason it persists today given the popularity of Chrome. Just as Microsoft is arguably the reason it started. (I suppose I could have been more careful in the phrasing of my initial comment since "is so useless" could imply both but I don't think it's particularly egregious.)

One thing I have always wondered about the story - were servers in the mid-1990s really sniffing user agents to decide what pages to send through? I remember most sites were static .html files back then.

Not sure if it's the server, or the javascript, but it was definitely a thing in the 90s.