@lamp they are in certain juristictions.

I.e. #Switzerland makes them mandatory and bans non-compliant plugs.
https://en.wikipedia.org/wiki/SN_441011

Also the #IEC made several good standards that do the same.
#IEC60320 for devices ( https://en.wikipedia.org/wiki/IEC_60320 ), #IEC60906-1 for sockets ( https://en.wikipedia.org/wiki/IEC_60906-1 ) and #IEC6309 for anything that needs more than 250V 10A 1L+N+PE ( https://en.wikipedia.org/wiki/IEC_60309 ).

The #EU mandated IEC 62196 "Type 2" connectors for BEV charging. ( https://en.wikipedia.org/wiki/Type_2_connector )