Is it? When you pay a certain amount at a buffet for unlimited food, they let you eat as much as you want at the buffet, but they don't let you bag it up and take it home. True unlimited costs a lot more.
There are ugly ways to cheat the system by replacing your stomach with a food sack and not chewing.
The buffet analogy isn't very compelling when ordinary people will watch video on their phones for long periods, easily using 3GB+ per hour.
I don't want more data, I just want flexibility.
(If we really want to force a buffet analogy, it's like living in a dorm with a permanent buffet, but you're not allowed to bring buffet food into the lounge or back to your room.)
Except you didn't? You paid for all-you-can-eat-on-a-phone, and 5 GB extra. So it's a dormitory with unlimited dining hall, but you can only take one plate a week outside of the dining hall.
For the provider, the point of this design is that there's only a certain amount that people are willing to download on a phone or eat in a dining hall. For the consumer, they don't have to count their data or their servings as long as they follow a simple rule - they get predictable billing.
That's one point of view, but you just banned unlimited-on-your-phone plans that a lot of people presumably enjoyed. If they change them to simple unlimited plans, you'll be popular. If they only offer limited plans now, you'll be unpopular.
We have a number of mobile services in the UK who explicitly offer routers with WiFi slots for replacing your home broadband with unlimited SIMs. I have used them in the past to replace the wired internet when there has been line maintenance that took out the broadband for a couple of days.
4G alone can get you a nice stable 100Mb/s.
You seem to be defending a shitty deal that happening in North America, without any clear reason.
There are ugly ways to cheat the system by replacing your stomach with a food sack and not chewing.