Educate me on wing tip vortex

I know what causes a wing tip vortex. What I dont understand is why plane designers dont do more about it. Most people know that planes that have wing tip tanks have better range since the tanks block the vortex drag.

So my question is why dont they just put end plates on the wings to prevent the pressure wrap around that causes the vortex an hence the drag? I know a lot of newer planes have the turned up wing tips that apparently does away with some of this problem since they go have better range. However it seems to me that a full end plate would do a better job like the old wing tip fuel tanks.

There must be a simple answer to this but I have not ever got a straight easy to understand answer.