I have a NAS, HomeAssistant, some random local-only IoT-type stuff, Plex, Pi-hole, and a handful of several other web applications running. Running my own PKI and having to manually distribute root cert to my non-domain PC let alone even think about how to install root certs on the various Android/iOS stuff I have: no thanks.
I can think of several scenarios where a small business (with no IT) would have local servers but no dedicated IT (and where a full PKI infrastructure is a big burden): for example poor internet connectivity, or very high bandwidth costs.