For me that is slightly disappointing, I find that there is some real character in that accent. From my (outsider's) perspective it is something classic to east coast American cities. An accent that brings forth unapologetic honesty and "bustin' your balls" kind of humour.

I have an old relative who has the classic, very thick Boston accent. It is always fun to have her say, "park the car in the Harvard Yard", and she is willing to humor us. You are correct that most younger people don't, though some have a less significant one. Accents are disappearing among the young, which is somewhat sad, albeit inevitable. Newscasters never have an accent, most characters do not (and when they do, it's a "difference" of some sort), and people move around too much for them to survive. A Texas accent used to be John Wayne, now it is used on comedy shows to represent the "uneducated, fat, cousin-marrying red-neck bumpkin". At least we have recording technology now, so future generations can hear them.

I moved from the southwest US to New England as a child, specifically Hartford, Connecticut. I definitely heard this accent… ‘cah’ for car.

Accent is defined based on where you grew up from age 10-12.

Distinctive communities get broken up now and disrupted by media.

I went to high school in the city of Boston with boys from all over the city. The different neighborhoods had different accents.