Machines are donated for a lot of reasons. In my area there are several retirement communities and very often when people pass, their relatives donate the whole household after they've taken what they want. Most of the sewing machines I've bought from my favorite thrift store have only needed a basic service to be in tip top condition. I've gotten 3 Singer 401s from this store. Now I've seen lots of dogs too, machines I wouldn't touch if they were given to me like newer Singer Inspirations and such.
Cari