Comment by 8474_s

Old code does acquire new bugs by sitting in your hard drive, since it interfaces with dozens of libraries and APIs that don't care about how well test the code is: every path of code is dependent on multiple components playing well and following standards/APIs/formats that old code has no knowledge of. Also, the mountain of patch-fixes and "workarounds" in the end force the programmers into a corner, where development is hobbled by constraints and quirks of "battle-tested" code, that will be thrown away as soon as it couldn't support fancy new feature X or cannot use fancy new library API without extra layers of indirection.