It gives them a good view of their surroundings, and they derive their superpowers there.
My cats usually prefer the window seat to actually going out...they have a petdoor for anytime they want out. i think mine just like to keep an eye out for any animal invading 'their' yard
I laid my head down in a window sill once to find out, turns out to be relaxing and warm from sunlight too...
They can survey their kingdom- it bolsters their feelings of superiority. *pets her kitty affectionately*
Because they're curious by nature and if it's a sunny windowsill then they'll be there all day!
they want to play outside