Unless in their own ROW, footpaths are part of the road reserve and share the same name and street numbers - that would make them much less "distinct" from the carriageway. Additionally, the tagging allows for stipulating which side of the road (or none at all) that the footpath is on - thus making the addition of footpaths adjacent to their parent road even more redundant.

Finally, footpaths drawn separately from the roadway is not common. It would be far simpler to remove the redundant footpaths and update the roads to have appropriate footpath tags than to go through the whole city and add new footpaths everywhere.