Barter is on the same boat, because your characters build relationships with traders on an individual basis.
It's entirely possible to have your top Barter character have a negative attitude with a trader, while everyone else has a positive one, and making barter global would let you completely bypass it.
That't true - but it's pointless in SP. Don't forget, you control the whole group. Every character is your character. When you're in SP the reputation with NPCs should affect all characters in your group, not only an individual one. That only makes the game more tiresome (for the reasons already stated above) without giving any real benefit. Again, not everything that makes sense for coop MP also makes sense in the same way for SP.
