You’re thinking a patch is text, but should think of it as a logical change. Unless the logic becomes part of upstream the patch is not tied to a specific point in “time”. There’s a cost to it, as you have to constantly rebase. This is the case with any non-vanilla distribution (e.g. Linux), although it’s also at a package level so you do this both for each package as well across every package. For well written code there’s reasonably low coupling so it’s less work to maintain.