RFC7766 "Recursive server (or forwarder) implementations MUST support TCP so that they do not prevent large responses from a TCP-capable server from reaching its TCP-capable clients."
My guess is that it stems from lax firewall defaults. "Allow port 53 - [tcp/udp/BOTH]?" (Yeah, I know that DNS can also work over 53/tcp, but it's rare compared to the 53/udp volume)
It's not as rare as it used to be a couple decades ago. If you block tcp/53 you will find a surprising number of things breaking as record sizes have increased over the years.
i think that is fine actually. however, if i would implement such thing i would probably redirect DNS traffic to my DNS server as long as you are not authenticated :)
large responses == some DNSSEC, some IPv6