It should be unimportant, but some people kick up such a fuss about having to learn new things or changing what they claim is 'natural' that it is important to a lot of people. Gender is both a social construct, and a very real thing that does warrant discussion.

The fight over pronouns is just the first step in "othering" trans people. It helps to reinforce the idea that they're strange, not like you, not traditional, not natural.

The next steps are to deny healthcare, access to equal treatment from discrimination, things like that. There are leaders in the USA making statements that transgenderism should be "eradicated."

If you aren't dealing with shit like this in your area, I'm genuinely happy for you and I hope this never comes near you. But for lots of people, it's quite a bit more serious than a first world problem.

If it’s so silly and unimportant why do people bitch and moan about using the pronouns someone feels comfortable with?

I say nearly this same thing, which is probably similar to what every generation says about the next one. Wait until they "grow up" and find out what real problems are. Your pronoun won't mean much if you lose your job and have to figure out how to pay the mortgage and for groceries before your kids starve.