This is just a guess, since I don't know the actual answer.
I use a vertical line tie, and a split ring, for all of my jointed swimbaits, because I think it really enhances the swimming action of the baits.
Except glide baits.
Since the idea of a glide bait is to move effortlessly in a S shaped path, a vertical line tie might act as a rudder, and inhibit the side to side glide a little.
The first bait I ever fished with that S shaped action was the original Gantrel, and it had a vertical line tie, but almost every other glide bait, except Jerry Rago's bluegill, has the horizontal line tie.
Also, I do a direct tie to the bait, with no split ring. I don't know if it makes a difference, but it's how I've always fished them. I think it might keep the pull point centered on the bait more, and that would affect the glide less, too.
Of course, I could be full of it. It wouldn't be the first time, and certainly wouldn't be the last. Hahaha