The problem with microaggressions is that they are so personal. If a person goes on a general, loud, racist rant you can challenge them and you will get support . But most of the time these smaller comments go unnoticed by others or misinterpreted as compliments or jokes, so if you do object, they just think you're being touchy.
I know this because I'm a Yorkshireman living in the Midlands who hasn't lost his accent in the 40 years I've been here. Not a week goes by without somebody wanting to know where my flat cap, whippet and racing pigeon are (I don't wear hats, I'm a cat person and I loathe pigeons). Then there are the 'jokes' about my supposed miserliness. Not to mention waiters who don't bring the wine list because they've heard me talk and assume I only drink beer. If I object, I get the 'only a joke' routine.
Lucky for me, I'm a thoroughly nasty piece of work, and generally folk learn to knock it off sharpish. For someone like yourself, a decent person, I can imagine it must be immensely hurtful, and when I overhear this sort of thing, I do get loudly tetchy with the half-wit who came out with the crap!