".com" looks professional and, more importantly, it very clearly communicates "this is a website address." If it were "bobbuilder.services" it could be a website, but maybe it's an instagram handle or something else.
Otherwise you are correct that it doesn't really matter. The main value of gTLDs is that we ran out of decent available .coms a while ago.
Single letter domains look cool (I guess) and signal that the org has the money to buy a premium domain. Similar to "mortgage.com"
