Unfortunately that means that my cell number which I wanted to temporarily park into VoIP while abroad is now permanently VoIP.
If you're lucky, the service you care about only validates at number registration time, not at text sending time, and you can get away with it indefinitely, I suppose.
Most of the reason to deny voip users is that many voip services give phone numbers away like candy and then those phone numbers are used to abuse other services, so checking the original carrier tends to be enough for abuse screening.
Some use cases want more though. Banking KYC has some back channel to get subscriber identification or be alerted when ownership changes; those institutions may be willing to pay for current carrier lookups and deny usage of numbers where they don't have a back channel to the current carrier.
Unfortunately, more and more services are declining to send to VoIP numbers because of seCurItY, so it's a game of cat and mouse.
Fortunately SMS is so expensive in parts of Europe and it's not allowable anymore to use SMS by itself for online payment authentication, and both issues combined have slowly been pushing companies to explore alternatives.
There unfortunately seems to be no such pressure in the US. Passkeys could solve the issue, but probably increase support request volumes enough for most companies to not bother unless forced.