That's not why. It's because you can can go to your Town/City clerk's office to get them.

Absolutely massive difference between dropping by the office in Rye and having a nice catch up with Donna while submitting your request as opposed to sitting in the Lowell DMV for several hours for the same thing. I've done both, it's 100% this.

Edit: I don't recall the exact differences, but MA also has more restrictions on what you can choose (repetitive numbers, no initial numbers, etc) as well as 6 characters vs 7.