I'm not sure I understand the concern - and that may just be naïveté on my part.
I had 3 grandfathered unlimited plans and I was paying $35/each... up until 10 months into the pandemic. I used these cards inappropriately. I used them to keep my 84yo mother online and connected in the middle of nowhere. (1 active, 1 backup, 1 spare). Eventually ATT just killed them with no warning.
Then I signed up for the "add an unlimited tablet for $20 to your main ATT plan"... I have 3, they work identically to the grandfathered plan, I pay LESS for them, and I've never gotten a warning or anything. I just bought 2 more over the holidays to so my niece and nephew can stay connected.
I was mortified when the grandfathered plan was cut off.... but... I ended up with the same service, zero problems, and a significantly lower bill.
So... maybe it's because people want the standalone account? I don't really get it. Switching to the $20 unlimited tablet plan seems like the way to go.