Because when you look at it, 
and 
are accessed easier and get the same job done. I don't feel as if there's any reason to not buy 
as it leaves you with other slots to buy items such as 
, 
, or 
The same on AP supports. 
with 
instead of 
seems better because I can fit more AP and healing in there than if I had 
taking up a slot
I think that the vision item just outshines the alternative just like you said.
It's a third shield and opens up the opportunity to have which makes spamming 
easier.
Depends on what you value, as in either have your support active items such as locket and redemption have a shorter cooldown as opposed to having another item that will give you some more of a bonus aside from health. Up to you and how you want to play it.
I used to like the other alternatives, but item slots are becoming more of an issue now and everything is already CD stacked like crazy so I feel like some of those upgrades lose value. I still try them out because I used to like them. But they just don't feel as good. Not very objective.
