They only fight that hard because they know the people fighting to remove "master" are (as a group) acting in bad faith.
On this and many other issues they tend to lie about history and language, extort those who don't comply with threats of sabotage towards their projects and/or careers, and will equivocate and dissemble whenever confronted.
It's perfectly fine want to use "main" rather than "master" (that is probably my preference). And it is perfectly fine to suggest other people do as well. But if you suggest it others and they tell "no" (politely or not), the right thing for you to do at that point is to mind your own business.
But a lot of people get very defensive about it, not just for practical reasons but out of fear of the slippery slope or the consequences of a perceived angry PC mob that can utterly destroy their projects and careers.