Software doesn't exist in a vacuum, and a change in the kernel or the C library could break something that used to work. Worse, you will probably discover this only in production because nobody is keeping tabs or running tests.
Worse, you could end up with another Heartbleed. Nobody bothered to look at that code for two years and the result was one of the worst security bugs in history.
Worse, you could end up with another Heartbleed. Nobody bothered to look at that code for two years and the result was one of the worst security bugs in history.