Medieval RTS games have a special place in my heart. But I'm almost convinced it's because of nothing but pure nostalgia, being the first RTS I ever played.
But no. It's the same reason I have a soft spot for the LotR movies, and for forests and earthy colored clothing in general, and wool clothing. There's something so... wholesome about it. Or simple. Or, je ne sais pas... preter-nostalgic?