It could be that some of the houses in question are rented out and the landlords/landladies simply CBA. It could also be that they belong to people who are not physically able to do it, so a gentle offer of help could work here - if you know that is the case. Perhaps, though, even the most able-bodied house-owners are just too lazy to be bothered. The council can and will cut the bushes back but they'll do it in a very utilitarian way and then charge you for it. Some of the spots are dangerous because the foliage grows out to such an extent as to make people have to leave the pavement, not a great idea if you are pushing a buggy, walking a dog or are not as nimble on your feet as you were (or are in a wheelchair, etc).