they're right on the property line so they drop on my neighbors property also, squirrels like to "hide" them up in the undercarriage of my neighbor's cars, they create tripping hazards, potentially damage my lawnmower if I miss any before mowing, etc.

and the branches currently overhang both my house and my neighbor's garage, so when walnuts drop they potentially damage the roof(s). I've hired a crew to cut those branches back but it's too much of a PITA to keep dealing with them.

I'll plant some other tree(s) that aren't so difficult to replace them.