The "problem" isn't specific to Moose. Perl itself provides even less.

Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun
— Larry Wall

Mind you, the internal setter in "conventional" objects is usually direct hash access rather than a method, but that's no more private that Moose's setters.

I don't think Detroit will start equiping odometers with knobs to set the value just because Moose cannot simulate it.

Do you anticipate that they will define a class that will be instantiated only once?

Or manufacture different mechanical/electrical counting mechanisms for each combination of engine, gear-train, final drive and wheel size, just so that the Odometer class getter can read directly from the volatile hardware register that counts directly in miles? Which would mean they'd need to double the number of counting mechanisms so that the register counted directly in kilometres on export models.

Because unless the miles/kilometres attribute was incremented directly by the hardware, something has to cause it to count.