Why mathematicians are boycotting their biggest conference

More than 1,500 mathematicians are demanding that their field’s most prestigious meeting be moved from the U.S.

Scientific American

Nobody will care if the conference isn’t held in Philly. Holding it elsewhere will probably make it a little easier and possibly a little cheaper for people to attend. I doubt mathematicians are part of the 1%, so cash and travel hassle should matter. And given today’s Internet, there’s going to be remote attendance which can happen most anywhere.

While it’s still convenient to gather together to discuss a field, it’s not crucial as it was in past times. Easier to do what’s best for the largest number of people.

Huh? This is primarily because travelling to the US is not worth the risk right now.
It's just grandstanding.They are mathematicians not political activists. If they want their organization to slide into irrelevance, getting involved in left wing (or right wing, but with academia it's usually left wing) politics is a great way to do that.
Anyone can be a "political activist". An activist is just an ordinary person who has had enough. Unless you believe the only valid way to influence political discourse is with money.
Sure, anyone can be an activist but it is clear that academia has been turned into an activist training centre. It is also remarkable how these supposedly intelligent people go astray when it comes to the causes they support, from supporting Hamas to defending those who'd throw them off high buildings or putting them against the wall if they got their chance.