Because that isn't how the new form is supposed to work. Observers are supposed to just fill in each section of the form and an overall mark is automatically derived. If they try to conform to a league average they'd have to go back in and start tweaking section marks, which means the marks wouldn't necessarily match the written text, at least not unless they adjust the text and that starts to fall into the realm of making it up to support a mark.
Also, don't assume that you are going to get extra marks for running further. I've seen loads of referees that are running unnecessarily because they aren't reading play, as a result they are then having to sprint to get back into position, and that is likely to be a negative rather than positive. More distance doesn't equal higher marks and it can be the opposite.
Likewise more cards doesn't necessarily mean a better mark than a game with no cards. If they were standard cautions that would / should be impossible to miss then you aren't going to be getting an 8, whereas if they took skill to spot you might do. Also, and we haven't seen the report so don't know, I've seen referees issue lots of cards that potentially was a consequence of either going with cautions too early or letting it go too much early on and then having to resort to cards to try and wrestle control back. Neither of those situations are going to be rewarded by a good observer.