Because this is a misunderstanding of LGBT+ "Pride". It is not just "Pride" in the common sense - rather it is in opposition to Shame.
Straight people have never been systematically subjected to shaming due to their sexuality or gender identity.
Straight people have never been systematically subjected to shaming due to their sexuality or gender identity.
Edit: My comment might seem a bit too negative towards LGBTQ and that's definitely not my intention, so I'd like to mention advocacy of gay marriage as a positive example - something that does clearly point towards a public image of very real honor and integrity for this notable minority group. It's hard to deny its significant contrast to the recurring image of "pride parades".
Your comment is not just too negative, it is simply wrong. Without Pride, same-sex marriage would never have been possible.
Definitions used for this sense of Pride (ripped from Google define, since they're good enough and I am lazy):
"Confidence and self-respect as expressed by members of a group, typically one that has been socially marginalized, on the basis of their shared identity, culture, and experience."
and
"Consciousness of one's own dignity" (Antonym: Shame.)
Note the Google definitions of Pride not being used in this sense:
"The quality of having an excessively high opinion of oneself or one's importance." (Antonyms: modesty, humility)
and
"A feeling or deep pleasure or satisfaction derived from one's own achievements, the achievements of those with whom one is closely associated, or from qualities or possessions that are widely admired."
[1] (And since the most basic way of countering social marginalization is to build up social capital, the "pride" attitude is something that, as a matter of fact, is directly detrimental to this goal. "Pride" is bad precisely because it corrupts and destroys social capital as much as shame does!)
People fighting for marriage equality were called worse things than insolent.