Ticketmaster did the same. They don't accept Google Voice numbers, yet my only number is Google Voice. The number tied to my SIM is an implementation detail that changes depending on where I am, but it's the only way I can get into that account now. My choices are to not go to events that are ticketed by them, or accept that I'll probably be locked out whenever I change SIMs.

SMS is literally the least secure form of authentication, because numbers expire after mere weeks, and get re-assigned shortly, within months, because of number shortage in many area codes.

Nothing like this could happen with any mainstream mail service like Gmail, where it's officially advertised that the accounts could never be reused.

The worst part about SMS is that not only is there the potential to be locked out permanently, but also you never know whether or not the service would allow login or password reset via SMS, thus, you never know if you're opening yourself to account takeover.