Oh, and when I'm doing something like this and max the line out, everyone else at home suffers and has to fight for bandwidth. My wife works from home as well so I need to be careful.
Precisely. While the average household usage might not be that high, that's not taking into account users where its more important that it works or that typically everyone will be using it at the same time.
I frequent linustechtips forum, the number of times people complain of bad latency in gaming, those are exactly the kinds of people where having more bandwidth than they need is the most useful, as it keeps latency down. Ideally, everyone would have more bandwidth than they ever need so buffering and packet loss would be rare, the majority of the time it wouldn't be used but its there to handle transients.
Another example I've used in the past is my own Fibromyalgia, the symptoms vary throughout the day so I might feel able to play a game RIGHT NOW and that game needs an update. (because you can guarantee auto-updates decided NOT to update that one game) That update now downloads in about 10 minutes max. When it used to take an hour or longer, I'd usually find brain fog/fatigue had kicked in by the time it had finished so I no longer felt able to play that game.
In a household working from home, its going to even be more critical as you point out, you don't want one persons usage to impact anothers.
I also frequent the Topaz AI forums, where a few people have suggested how useful it could be to upload a video to a cloud service to run the AI upscaling. There is little benefit to that if the upload takes longer than the upscale. I myself had to avoid any long upscales during the heatwave, if I could run it remotely then I wouldn't have had to (though in my case the cost would outweigh the benefit, but to a professional not so much).
There's probably a multitude of things we've not even thought of yet that might make it even more useful. YouTube only became a thing once enough people had fast enough broadband to stream video, then the other streaming services.
To suggest that "nobody needs faster than x" is extremely short-sighted, its literally the progress in speeds (both broadband and computing) that has made the Internet what it is today, the good and the bad. Every technological evolution has been mocked as "but nobody needs that", and almost every time we've found uses for it. Because finding new uses is a process of playing with what we have to see what it can do.