Take a look at the following comment from Searge in MC-82854 (about different stairs rotation in snapshot 15w31a):

searge
We unified the orientation of many items in the inventory

So, by that I expected that a few items (not only blocks) would be changed as well, so that all of them face the same way. And that's not what happened. For example, melons and glistering melons face opposite directions from each other since they were added, and that has never changed.

It's right that it's much harder to do it with items, since you can't specify which direction some of them - like a melon or a steak - are pointing to. So, I'm not asking that all the items face the exact same way - just that the similar-textured ones follow a pattern, like the melons.

Despite being that way since they were added, I've never found an opportunity to report that. But now that they're trying to "unify orientations", I think this makes sense to be reported. I did not play Minecraft when these items were added, which was very long ago. So, I don't know of any intended reason for them to face different ways. But if there was a reason, sorry, I didn't know anything about it!