But if 2014 Thanos was killed, everything in the first movie is different.
Ooo... pretty butterflies...
Seriously though, many timelines were created in this, and the main timeline still has a dead Vision. Simple as that.
I still don't understand why they simply undid the snap. They could literally do anything they wanted with the Gauntlet (including bringing back Uncle Ben without changing history), and that's all they did? They need better imaginations.
Just because one had the power to alter things does not mean they should alter things.
If you choose to revive someone from the dead but not someone else, you would be seen as something akin to a jerk.
Also who is to say that vision isn't in a lab in wakanda being analyzed and attempted to be repaired? Infinity war determined that if the mind stone were safely removed and his mind recalibrated as they were starting to do, then he should for the most part be who he was as his mind was an amalgam of different sources..