But they're not using 'rationalism', which is the specific thing term you mentioned. And lots of other fields, likes economics and decision theory, use 'rational' and that term covers the core interest of the 'rationalist' community.

Naming is hard, it's common for lots of people to make 'mistakes' similar to what you've pointed out, and it seems like a very minor criticism of what is otherwise a great group of people united by an interest in important and useful thinking.