Sent the in-laws on a cruise a number of years ago. Unbeknownst to us it was a designated "Gay" cruise. If you didn't know such things existed, there are several groups nationwide who try to organize LGBTQ+ focused events. First, obviously, is to make money for said groups, but second is to create a safe/welcoming atmosphere for their target clients. Important detail: father in-law is not exactly down with "the gays" and his only real complaint is similar to your paragraph: why do they need to advertise it? Just be gay in private and I'll be straight in private.
Now, the interesting thing about boats is that you are a set population once you leave port. Meaning the gay folks, not the straight folks, were the majority once this particular ship set sail. Suddenly my father in-law was the minority. He reacted as you might expect: "you 75%+ boat population stop doing gay things in front of me." We tried to explain to him that most of these people have to constantly watch what they say and do every minute of their public lives. Some have lost family, friends, and their religion. Others are probably dealing with a lifetime of guilt and shame. Suddenly, on this little boat for a short period of time, they can let it all go because the majority is just like them. Imagine the feeling and imagine how fortunate you are to rarely ever have to feel that way for being straight.
The point I am trying to make is that most of these people have few safe spaces to actually live their complete life in public because they are the overwhelming minority. Parades, flags, or anything else that supports their life journey is just a brief moment in time where they can feel safe, comforted, and free. That's all it is.