This is a good point. The problem is that programming is like gardening. You can't expect a garden you plant one year to be as beautiful the next year without a little work. You need to weed, prune, replant, and fertilize it.
In programming we need to patch and refactor. It's all for the best really. The way to sell refactoring to a customer is to tell them that sooner or later, without it, they are heading for a meltdown. It's not because the program was bad when you wrote it, it's just that entropy is the way of the universe.
No application, especially a web app, can withstand time without maintenance.
Also no web programmer can survive on new projects alone. Eventually maintenance and upgrades come into the picture.
If your clients don't understand that, then you need new clients more than your current clients need you. And you can quote me on that. I've been building web apps for 12 years. None on the sites I built 12 years would still be relevant or working today without upgrades.