I would speculate that Automotive speakers need to be built physically stronger to withstand the jarring environment, heat and cold of a car. I've seen complaint about Nakamichi auto speakers failing due tho the stresses encountered. I did an earlier post about a 5.25" driver in a pair of Michaura M55's I bought used. The magnet structure appeared to be jarred out of alighment causing binding in its positioning spring. I think this happened during shipping.

Mark