But they do control it. This is a big problem in Europe. You can't get one on a prepay contract with most of the local carriers, they limit the phones they will allow them to be used on to only locally sold versions, and they often charge for a SIM swap or limit the amount of times you can change phones per month.
None of these limitations were present with physical SIMs.
> You can't get one on a prepay contract with most of the local carriers,
To be fair, on this particular point it can be incompetence. Telecoms have absolutely no skilled engineering capacity (third-world body shop is as good as it gets) and the entire thing runs on decades of duct tape and outdated, unsupported and vulnerable software.
The most likely reason for this not to be possible on prepay is that prepay and postpay are managed by completely different systems and making the prepay system work with eSIMs would be too difficult, or maybe they tried, it broke, they rolled it back and have a "TODO" to fix that (of course the TODO will never be addressed).
For GSM carriers, esims add a layer of complexity because they are apparently bound to a phone. As you probably know, SIM cards can generally be swapped in.
This makes provisioning more complicated, because roaming. I never bothered to understand how GSM addressing and routing works, but I'm assuming this requirement makes things even harder to deal with.
In Thailand anytime a new SIM is activated an ID check is required. In the past I kept a SIM and I used to just move it between phones. Now when I want to move my eSIM between phones I need to go to the shop with my passport or do a video call with tech support and show my passport to them over the call. Such a pain in the ass.
None of these limitations were present with physical SIMs.