They won't do it, especially not after the most recent changes. I agree that it's awkward, and it doesn't help that all of his abilities aside from his Q that feel like they summons a crossing guard to escort your enemies away from it.
But the issue is you get to a point where Swain's too good at being a lane bully to melees, and they have to balance him around only that and he becomes utterly unplayable against range. His Q already has a disproportionately high access to melee champs, and now minions aren't proper cover against it. Letting E be double tapped leads to Swain excelling a lot more at close range fighting, where people won't have any real agency to avoid it. He simply has to let a melee reach the border of the his E range, then advance towards them. You end up with a degenerate playstyle where on a melee you either never enter into Swain's E range or pretty much guarantee taking all 3 spells/ autos while he has time to back off. Add in getting 2 soul frags for that for healing and mana, and a nice splash of electrocute, and things will have to start getting pruned back.
They've side into having Swain be the one that has to maintain distance early, which is easier for him to do and lets him not be so specialized into fighting melee that he has to be ass at everything else
