I understand some people don't like change, but if changing "man" to "person" upsets someone then it rather feels like they don't like sharing.
What we are upset about is that this is being "forced" on people (Soon, watch. Probably already happening in schools, though). And likewise, that it's being done under the guise of some sort of greater-good when it seems rather petty and won't really change the day to day issues facing women and black people.
We're also upset that this is effectively taking a step in the opposite direction to real equality.
Additionally, I could care less that we stop using "man" and "white" etc. What does bother me is that there is this nagging feeling that this is being done purposefully to upset certain groups (which we can then turn around and say "look, see, they don't like their white/male power being dismantled, they are race/sex-ist and look how much we're defeating sex/race-ism!").
Everyone already knows that "manmade" is an inclusive term, if women or children makes something it is still "manmade" so there is no need to update the term. If you say that wording matters, then you also should be against the term "toxic masculinity" since it is a very aggravating term, there are so many less aggravating terms that could be used for that phenomena.
Edit: If you don't understand how expensive these things are try to think about why USA still uses AM/PM and the imperial measuring systems. It is trivial to switch on all new products, right? Well, of course that isn't true, changing language is as I said super expensive which is why it isn't done often.
There's a huge overlap there.
What bothers me is how much this is an VERY regional issue, specifically, USA-based, yet it's being imported wholesale across the entire Western world, when it doesn't make any sense.
It's sad seeing locals making BLM protests when we have <10 black people in the entire country, or German bloggers who suddenly find themselves questioning if noun articles are the cause of toxic patriarchy.
The empire defines the rules, the provinces follow. I find it positive because it makes these relationships very obvious, nothing is hidden.