Eh, grills are kinda meh, imo. They do protect from impact, but that’s not as likely as you’d think. But dust and debris? Grills are useless. You need something that will prevent things like that from getting on the speakers and causing deterioration over time.
Unless you’re including screens and meshes in grilles, and some folks do.
But yeah, it’s cheaper, and people like to see the speakers, so it helps sales. No bullshit, I’ve lost track of how many people have been weirded out that my car system is covered by a screen. They think you have to see the speakers or they’re somehow fake or made of cheap materials. Like, motherfucker, I built that damn box for one thing. But car speakers are exposed to sun and heat and even worse dust. Not having a screen over them is silly.