I think they ban cameras to 'encourage' people to buy photos sold by endorsed photographers (who only operate up to 1pm so they take most of their pics when you don't know the track and are on cold tyres- dangerous if you ask me). But I'm sure they'd say it's for 'safety'. At Tassie track days you can use cameras but the fit-out must go through scrutineering, but then our track days are not-for-profit efforts run by the clubs for members, whereas PI Ride Days is a very commercial operation (you can buy tyres, clinics, pay for suspension set-up, photos etc).
I'm not knocking that, it's just how they do it.
My Hornet friend had a big off at Eastern Creek a few days after this- exactly what boney said about speed differential... someone breezed by him on the straight (on an R!) then jammed on the anchors and turned in early for the very fast Turn One, just as he was trying to get through. I really keep my distance in the fast turns at track days, unless the other rider is someone who REALLY has shown they know what they're doing.
If you want to get past at all costs, you go racing.