My guess? Tradition
It’s very, very tough for some people to let go of things simply, “because that’s the way it’s always been.”
It doesn’t have to be a flag. It can be anything as simple as, “that’s the way I’ve always put my clothes on or cooked broccoli or parked my car,” or, “that’s the way school/church/gov’t has always been” or whatever.
Change is just plain “wrong” as the default.
Evolutionarily speaking (or natural selection wise speaking), keeping things the same as has worked before is usually safer than trying something new, so it’s a common human response. Then any sort of reason needed is thought of to support tradition. Any other reason proposed is scoffed at.