Because auto-sellers don't want to work both days of the weekend.
Let's say I run a liquor store. I get together and collude with all my liquor store running buddies and pass a law that says liquor stores can't be open after 5pm.
Ta-da, we all get to go home at 5pm. We don't lose any sales to people open after 5pm, because no one is allowed to do that.
Texas had a bunch of restrictive laws about Sunday called blue laws, the last one left is for liquor sales.
Used to be you couldn't sell cars at all on Sunday, but they added this "either or" clause a few years ago for some reason. Dealers claim having to be open 7 days a week would drive up costs...go figure.
Let's say I run a liquor store. I get together and collude with all my liquor store running buddies and pass a law that says liquor stores can't be open after 5pm.
Ta-da, we all get to go home at 5pm. We don't lose any sales to people open after 5pm, because no one is allowed to do that.
And if someone wants alcohol after 5pm, fuck 'em.