In OSM, access tags such as foot=no should strictly be applied only where there is a legal restriction. See https://community.openstreetmap.org/t/poll-should-streetcomplete-disable-the-are-pedestrians-forbidden-to-walk-on-this-road-without-sidewalk-here-quest-in-the-uk/118387 for an example of a discussion on this subject. So foot=no should only be added where there is either a sign forbidding pedestrians (Bulgarian type В12, see here https://bg.wikipedia.org/wiki/%D0%9F%D1%8A%D1%82%D0%BD%D0%B8_%D0%B7%D0%BD%D0%B0%D1%86%D0%B8_%D0%B2_%D0%91%D1%8A%D0%BB%D0%B3%D0%B0%D1%80%D0%B8%D1%8F#%D0%93%D1%80%D1%83%D0%BF%D0%B0_%E2%80%9E%D0%92%E2%80%9C_%E2%80%93_%D0%9F%D1%8A%D1%82%D0%BD%D0%B8_%D0%B7%D0%BD%D0%B0%D1%86%D0%B8_%D0%B7%D0%B0_%D0%B2%D1%8A%D0%B2%D0%B5%D0%B6%D0%B4%D0%B0%D0%BD%D0%B5_%D0%BD%D0%B0_%D0%B7%D0%B0%D0%B1%D1%80%D0%B0%D0%BD%D0%B0_%D0%B8_%D0%BE%D1%82%D0%BC%D0%B5%D0%BD%D1%8F%D0%BD%D0%B5_%D0%BD%D0%B0_%D0%B2%D1%8A%D0%B2%D0%B5%D0%B4%D0%B5%D0%BD%D0%B0_%D0%B7%D0%B0%D0%B1%D1%80%D0%B0%D0%BD%D0%B0 ) or because it is mentioned as forbidden in the traffic law. Thanks Dimitar for mentioning the new rule in the traffic law! Afaik in the Bulgarian traffic law, pedestrians are forbidden only on motorways, and now in tunnels and on bridges without sidewalk.
A properly designed router should know the legal restrictions (so should not route pedestrians over motorways and bridges/tunnels without sidewalk) and otherwise should set its own rules that help pedestrians choose safe routes for instance by strongly discourage routing via major (high-class) roads and road links without sidewalks. This is the router's job, and not our job as mappers. See https://wiki.openstreetmap.org/wiki/Tagging_for_the_router