Why there is no better screens in VR headsets ?

[mrnoone]

I made a research and saw that these resolutions which cause screen-door effect.
Oculus : 2160 x 1200 HTC Vive : 2160 x 1200
Maybe some or most people will say that "there is no screen-door effect *** are you talking about ?" but i just want the answer of my question.
I know that we can produce 4k screens for mobile phones maybe we can even produce 6-8k who knows.
Then why we are not using 4k or more resolution screens on these VR headsets ?
Thank you for all answers.
Im not english so sorry for my mistakes in writing.

 

[mrnoone]

Yeah, recently someone from Reddit sent it to me.But it still doesnt explain why known headsets doesnt use 4k or more higher resolution screens.

 

[mrnoone]

Actually i thought about it and its completely possible just like Pimax is doing.If big companies had done it, it would have been done already.