In my personal experience, when you write code which caters to many legacy systems, your code will likely end up... * adhering closely to well-regarded coding

In my personal experience, when you write code which caters to many legacy systems, your code will likely end up... * adhering closely to well-regarded coding practices regarding naming, typing, modularity etc. * being more standards-compliant (except in clearly-identified locations) * having more robust abstractions * exhibiting less bugs (in particularly on modern platforms) * having a more robust build system * being automatically compatible with future platforms, or at the very least exceedingly easy to make compatible which is a good thing. (But this may not be true if you cater to just a few legacy systems, because then you might make do with a bit of idiosyncratic combination of fudges and hacks.)