When T-Mobile moved to unlimited with the ONE plans, they gave You "unlimited" tethering at "3G speeds", which turned out to be 0.5Mbit/s, an unusably slow speed in 2018.
The Magenta plans gave you 5GB-50GB of full-speed tethering before dropping you to "3G speeds". The current Go5G plans are similar, with a limited amount of usable tethering data before you're, for all practical uses, cut off.
Before the ONE plans, there technically was no hotspot usage limit, but since you had a limited amount of high-speed data, your hotspot was effectively limited to whatever your plan gave you.
All the US carriers limit hotspot usage, partly to prevent someone hooking up a computer to download 50TB of pirated movies while clogging up the bandwidth for everyone else on that tower, and (moreso) partly because they're greedy.
3g speeds are fine, no clue what you’re talking about. I literally tether all the time and when I hit the limit it’s still completely usable, even for YouTube. And getting to that limit is well above the 5gb from ATT. Like I said, att is shit, T-Mobile doesn’t do this and hasn’t for years.
Literally every carrier on the planet limits hotspot data in some manner. This isn’t a US thing.
Net neutrality isn't going to do a thing about this kind of stuff. In a best case scenario, you'll end up with overall data usage limitations - no more 'unlimited mobile data'.
ISPs meter data usage because it's pretty much the only way they can impose some form of limitation on a finite capacity to provide such data to you and other customers - other than data rate limits (read: slower speeds). They can't guarantee data rates in almost any setup, because ultimately, while 'data usage' is a bit of an artificial construct and 'data' is not in any way finite, the pipes that deliver the data certainly are of finite capacity. Mobile data capacity - and in fact, any wireless medium - is a shared medium, the more people try to use it simultaneously, the less pleasant it's going to be for each individual user. Ask Starlink users in many US areas how overselling limited capacity impacts the individual user.
Mobile data usage also has different usage patterns than if you're hotspotting your PC. You're not going to download massive games or other bandwidth hogs to your mobile. You probably won't be running a torrent client either. So they can give you unlimited mobile data because you're simply not going to put as much of a strain on the infrastructure with pure on-device usage than you will with hotspotting.
This isn't a defense of what AT&T is doing. But net neutrality isn't going to force them to suddenly be all ethical. It's not going to make them provision infrastructure that doesn't fall over at the first signs of higher-than-usual load. And it certainly can't change the physical realities of wireless data communication. In an ideal world ISPs wouldn't be so greedy and/or beholden to greedy shareholders to be cutting corners, and instead provide sufficient infrastructure that can handle high demand.
And to those who are talking about their workarounds: you may not like it but you've signed a contract. That contract stipulates acceptable use, and if you're found to be breaching the contract terms, the other party is within their rights to terminate the contract. Again, in an ideal world these contract terms would be more balanced towards the needs of the customer, but in the meantime your best recourse against unfavourable contract terms is to take your business elsewhere. And if you can't do that, everything else is at your own risk.
But where are they offering it? Big cities and densely populated areas where people have options and therefore won't swarm to the product? Or are they offering it in small, remote towns where there's not a lot of competition?
Where I live, mobile home internet is not available outside of metro areas and larger cities, and in the regions mobile towers are chronically underprovisioned and overloaded.