I don't understand why voice calls aren't just a standard and required part of the 4g and 5g specifications?? Did they really design and implement 4g and 5g assuming 3g would never be shut down, ever?
They are, it's called VoLTE/VoNR. For whatever reason telcos add whitelist schemes to prevent phones from making voice calls, even if they actually support it.
Therefore, it is not compliant with the legislated requirement that all phones must be able to make emergency calls on any network. By blocking it, the telcos cover their ass, at the expense of the consumer having to upgrade - even if said phone was actually possible to make work with a bit of software tweaking/upgrading.
Not to mention that there's an alternative way to fix this problem - create an app to make emergency calls over data network, which would work in theory (it's only voip that isnt standardized). This is exactly what india did, with their Jio app.
I don't know exactly, but I think they prioritised the release of the LTE standard for data networks, and thought that voice could be sorted later.