Because they're obviously crazy.
Last year it was a retarded baby sparrow.
This year it's the likewise intellectually delayed robins.
Always the slanted part of the bowed window that faces the church.
Don't know if it's the way the trees in the front of the house reflect on that particular window, or if the rail on the porch is particularly handy as a launch pad, or if it's the residual bird poop calling out to them.
Whatever it is, they seem excessively fond of that bit of rail, and that angled window.