If you buy a house that is not new, and your toilet is working, replacing it will be definitely not on the top of your list. And since other renovations - which usually matter much more for people take priority. Add to that the fact that "we recently did a new kitchen" sounds much better in conversation that "we recently bought a toilet seat which costs only a little less than a used car" - and here you go.

The factor of the cost is important too. For $1700 I could redo a whole room - why would I spend this on a toilet when I already have a perfectly working one? Of course, if money is not an issue, it's different - but for most people money still is the issue.