hudebnik | Terminology: car-top carriers

Our car-top carrier hasn't had a functioning lock in several years, and this summer we finally decided to get a new one (since getting anything repaired is an uphill battle). So I searched "car-top carrier" in Google Maps, getting a list of a dozen nearby auto-parts stores that mention car-top carriers on their Web sites. I called the nearest store of a major nationwide auto-parts chain.

"Hello? I'm looking for a new car-top carrier, or perhaps to repair the one I've got."
Silence.
"Let me get you to someone who can help you."
"Hello? I'm looking for a new car-top carrier, or perhaps to repair the one I've got."
Silence.
"A new what?"
"Car-top carrier."
"What's that?"
"You know, the container you attach to your roof rack to carry extra luggage."
"Oh, let me get you to someone who can help you."
"Hello? I'm looking for a new car-top carrier." [Maybe the mention of "repair" was confusing them.]
Silence.
"A new what?"

What's going on when multiple employees of an auto-parts store, who in my experience are generally hired for some interest in and knowledge about cars, don't even recognize the phrase "car-top carrier"? It's not like they've gone out of style: I see them around my neighborhood every day, even outside summer-vacation season.

We did some Web shopping, and eventually

shalmestere bought one through Amazon, mail-order: it arrived a day or two later in a cardboard box the size of a bathtub, and we used it for a trip last weekend. It has some design flaws, which I discussed here, but it's better than nothing, and arguably better than the old one without a lock.