Hi Tanya,
Firstly and mainly because they are not paths. Not every trodden bit of nature is a path. If you look carefully at satellite images, or around you if you're local like me, you could discover hundred of 'paths' that are not footpaths.
Secondly because these ways mapped as footpaths cross protected nature, where you are not allowed to walk so wildlife can have their own space.
Thirdly, connected to the previous, because footpaths in Openstreetmap are used by navigation software and could send hikers inadvertently into vulnerable nature. Removing the footpaths helps protect our nature and prevents disappointment with hikers planning for a great hike with software.
Does that answer your question?
Regards, David