Why should misgendering be treated with more respect than the respect given?

You imply they intended some disrespect. They used a default pronoun and when asked to do otherwise they obliged, despite being immediately accused of doing a shitty thing. Folks are being offended on behalf of a person that hasn't said anything about how that person feels one way or another.

A "could you use a non-specific pronoun instead of masculine when you don't know" might have gone a long way, but implying some mundane default use of a pronoun is malicious and shitty is just a really excessive amount of vitriol when absolutely nothing was meant by any of it.

I know about singular they, but I don't like it. Perhaps because there was a movement in my childhood education to "correct" the use of singular they, as noted in that wikipedia article there was significant pressure for hundreds of years to make people not use plural pronouns singularly. I for one wish that a singular, human appropriate, non-specific personal pronoun emerged because singular "they" just grates my nerves.