The video processing isn't good enough.
Laptops rarely see enough juice to run real quality movies on large TV screens.
This has been raised a few times, I was even looking at a box of old computer parts with a brand new graphics card and it wouldn't have enough juice to deal with high quality video either.
What I bought to fix the issue was a WD live box to run an external powered HDD for video file source. Hasn't missed a beat.
The only thing necessary for the triumph of evil is for good men to do nothing - Edmund Burke