How can carrier limit hot spot connections

I have encountered this question and in accepted answer there is information that doesn't click

For instance, the iPhone 5 should theoretically be able to handle up to 14 connections, but both AT&T and Verizon limits it to 5.

How can carrier limit hot spot connections?

To clarify I own iPhone that uses sim card, and live in Europe.

Solution 1:

It's baked into the iOS as a configurable number and the carriers submit carrier profiles that contain their preferred limits.

When the first iPhone came out there were legitimate concerns it would crash the carrier since they didn’t have controls to manage usage. This close alignment between the carriers and Apple exists to this day granting them control over many aspects of the radio configuration.