Think of it as providing a discount for going v6 only. Every single provider is charging you to have a v4 address. They aren't charities. Some providers just let you opt out of paying for that.
I think v6 only server but also have like NAT64/DNS64 (or just a HTTP proxy) for v4 internet access is practical for now. Even if dedicated IPv4 address isn't needed, most people may want v4 internet access.