Why is checking of commonName for hostname disabled?

[londondaintta]

I'm fairly new to TLS. I've been trying to connect over TLS and was confused why it wasn't working. I now see that it was failing because my certificate only has a CN, no SAN which is explicitly disabled here https://github.com/encode/httpx/blob/master/httpx/_config.py#L138. curl doesn't seem to have this behaviour and neither does ssl.create_default_context so I am curious why this is explicitly set?

EDIT: After some research I can see that CN as a verification method has been deprecated for some time.