Re-tracking is great if the coaster is so beloved (or in the case of Hulk) something that they really can't replace with something else because of existing infrastructure/licensing. When it comes to replacing a coaster that has lower ridership, there's no reason to spend millions on an exact replacement (which will not draw much more ridership and isn't really "marketable" as a new coaster) instead of spending the same (or just a little more money) to build something brand new that is a new ride and will draw guests. How do you market "it's our new coaster that's exactly the same as our coaster you already road, but this one is brand new!".
The GP won't think "Kumba was a little rough, but this new version of Kumba will be so much smoother! Let's get to Busch Gardens to ride the same coaster we already rode, but just a little smoother!!!"