You spend a little now to prevent the hypothetical need to spend more later - a need that may or may not arise. For me, I just have one bike. I don't want to compromise with a beater bike that doesn't have the various things that make the ride practical and comfortable for me. If I bought a beater and rode that I would always be missing my real ride and its amenities. So I know already that I would probably keep adding stuff to the beater, so it becomes less and less "beaten".

A trap to be less than frugal and simple. I'll just protect my good ride best I can.