As near as I can tell from observation, elongated toilets greatly outnumber found toilets, for good reason as you have pointed out. However, most of them are the low type rather than the better higher ones. Some people, as they age, require higher toilets. I don't know why the original equipment ones aren't higher.
Water saving toilets are better for environmental and also other reasons. However, replacing a toilet to save water might not be justified by economics alone, depending on circumstances. Figure how much, including parts and labor, it would cost to replace a toilet to save water. Then, figure out what your interest rate is. It should be a minimum of 4% if you have no debts, i.e., car loan, home mortgage, etc. If you do have such a debt, use that as your interest rate. Then multiply the total cost of the toilet by that interest rate. Unless your annual saving in water exceeds that result, replacing the toilet could not be justified if economics were the only reason.
Here is a theoretical worked example. Suppose that your interest rate is 4% and replacing the toilet cost $1000. Multiplying $1000 by 4% equals $40 per year. So, unless your water bill were reduced by at least $40 per year, replacing the toilet could not be justified if economics were the only reason. A similar approach is also valid for other investments, such as replacing a refrigerator or furnace with a more efficient one. The payback years method is not valid.