I'd rather enjoy what little life I have left than spend it avoiding all the things that are supposedly going to shave years off my life and spending the entire day standing. I got a nice cushy knowledge-worker career precisely so I wouldn't spend the entire day standing while flipping burgers or digging ditches, thanks.

Besides, I'm in pretty poor health due to my own lack of attention to it and of all the things I could bother with, "standing all day at my desk" is pretty far down on the list of what would actually make an important improvement.

Plus, you know, I'd rather spend thousands of dollars on something else. A desk of any useful size that is able to bear any useful weight load on it and is also adjustable in ranges enough to go from sitting to standing are incredibly expensive. I'd rather use the money to pay three or four months of my mortgage.