They adjudicate on everything else, they manage to work out knock ons (not to a 100% strike rate either might I add,) so why would they not grasp forward passes with similar accuracy?
Every third or fourth pass out of dummy half is forward now, they may as well rename the position quarterback.
For the Nth time - they can't grasp forward passes because forward passes are lateral movements in 3 dimensions plus time - you need cameras and software capable of making a 3-dimensional assessment of the entire playing volume (~116m long, ~70m wide and ~10 m high) then determining whether passes go forward relative to the passer - it just can't be done with the technology they have. You can't use the elevated centre-fixed isometric views we have on telly, front-on views are useless, and side-on views are only workable if there is a camera parallel with the football 100% of the time, which there isn't (and even if there was, it wouldn't take into account the elevation of a pass).
I provide this link every time:
https://www.youtube.com/watch?v=box08lq9ylg
Knock-ons are not the same - it's only a matter of did he touch it and did it go forward to the ground or the opposition? You can argue that 99% of touches are correctly observed, the only grey area really being did the knock "go forward'. In that respect, you are talking very small movements of the ball, some 1-2m max in normal circumstances, with an error touch and the following landing. The ball does not typically transfer from one player to another on his team.
So taking your point, that there isn't a 100% consensus on video knock-ons, imagine how much worse it is when you apply that grey area "did it go forward?" to passes, of which there are hundreds (thousands?) per match and very many of them with a wide grey area of interpretation - passes covering 3-15 metres across and +/- 3-4m forward/backwards.
In fact don't imagine it, cast your mind back circa 1996 when they did rule on forward passes and it was pure pot luck. They didn't remove forward passes from the video ref for the fun of it, they removed it because it was proven to not be consistently reviewable by someone on video.
You would think, that with the video bunker and the amount of decisions that do get sent for video review, they'd send up forward passes if there wasn't some strong disincentive to do so. Some people have the logic all backwards - they don't send up forward passes precisely because they can't review them just like they do knock-ons or offsides. They aren't doing it for the spite or fear of it - would be the first time in a long while that anyone would have accused the refs or the bunker from under-adjudicating a match!