Telecoms lobby against this because they generate big revenues servicing SMS spammers whom end-users aren't able to effectively block since the ID is trivially spoofed.
I don't use WhatsApp, so with people who do not have Telegram I use SMS. The more annoying and conotated with spam SMS is, the more pushy people become with insisting on WhatsApp. Luckily I'm often in a position to absolutely resist, but I can see how others, such as job hunters or Tinder hookups, would be pressured into installing the spyware.
This is not being done by Facebook/WhatsApp themselves, but keeping SMS annoying is certainly in Facebook's interest.
They haven't gotten to blocking messages that don't register but have raised the fees and fines for folks who don't register and they're able to track down.
It’s profitable on multiple levels to allow this, so corporations ensure the political class doesn’t enact legislation for consumers.