IT and telecom tend to have an ultra conservative if it’s not broke don’t fix it attitude. It won’t get deployed until enough customers ask for it or it’s required for something important.
Most v4 support is through a gateway. You can't tell the user's IP address from the wrong side of the gateway, for example - only the gateway's address. The user isn't on v4, the gateway is.
Yeah, so you still reach the user, it's just probably less efficient than the all-v6 route.
Edit: Oh, you mean if they want unsolicited inbound traffic? Sure, but that's only a thing for services. I mean you can have a default-allow firewall to home devices but really shouldn't.