A handful of raisons
I think the last time the North Slope of my yard was mowed was when the builder was trying to sell the house back in 1982. Eventually, I even gave up trying to mow a path along the property line because saplings and groundhog holes made it too difficult. So now this small part of my property is experiencing secondary (or more likely, tertiary) succession.
There's a lot of poison ivy growing all over the property, so I rarely step into this area in the summer. It's much safer to enter in winter when there's snow on the ground (and, of course, the leaves have dropped). The other week, after the storm (which gave us more snow while points south got more ice), I walked back here and was somewhat amazed (yet not entirely surprised) at all of the piles of deer scat lying on the snow. Of course, the rest of the year the piles are hidden in the leaves and growth. Several (about three to six) deer are making themselves at home here, ranging across the road and up the hill to down back across the stream.
The snow also reveals more clearly the wanderings of the deer (as well as various other critters). I can see where they've been lying down, and I can see that they sometimes walk through areas that I would prefer to walk around. I see that they come right up to the house, but they usually don't get close if I'm around with my camera handy.
To return to the title of this post, I don't mow all of my property because I'm bone-idle, and because I have better things to do with my time. I don't want to burn fuel needlessly, nor pollute the air any more than necessary. And because by not mowing, I leave cover and food for the birds, critters, and deer. And I have a more interesting area to walk around in.