>>17980237 (OP)
Most iconic flags were not the result of people going "hey, we should have a flag, let's design one". They developed in random, organic ways, usually had many differnt versions until they got standardized. That alone took care of the "meaningful symbolism" part.
Most of the modern flags people don't like are made by local regional governments at peace time, and they look for important things in their region to put on the flag, but these things are usually boring. Most regions have some dominant river or mountain, or an industry they are famous for. Than you have to make a minimalist representation of that, because all these people read 'Good Flag Bad Flag.' Of course they produce lot of boring, generic flags.
In Europe, most settlements have a coat of arms, and when you look at the CoAs of a lot of small towns, they quickly get very boring and generic. Most of those places have no intersting history, so they are usually combination of pictures of churches, crops, some hills or rivers, agricultural tools, maybe local wildlife etc. At least they look nice, now imagine if you had to simplify them to flags with only 3 colors.
