most highway=* values are already assumed to be public transport accessible by default, therefore it's not necessary to tag this.

See https://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access_restrictions#Worldwide

In my view we don't want to be tagging every single road as hgv=yes, psv=yes, bicycle=yes, etc. that's just noise.

Where there are bus lanes we should be indicating that with the relevant tagging, or where it could be ambiguous like highway=pedestrian we should specify or where there's signage like no access, busses excepted we should tag that but otherwise for regular roads we shouldn't usually tag psv=yes.