With larger grids, especially at race starts, there would be a lot of bumping and barging or evasive manoeuvres nothing bad just race stuff which would mean people being put off onto lines that would cause the HLVC to kick in. This could go on for a large part of the race which would mean you'd probably spend the same about of time checking for actually HLVC breaches and not just being pushed off line.
Think of somewhere like South City where touching a wall invalidates the lap, times that by a full grid and it could be busy. It’s a nice idea but you can see it could be just as time consuming as checking replays, it might be easier for people to just report anything they see that could be illegal, would be much easier to check out.