in the USA those with TSA Pre get an experience mostly on par with Australian (and Canadian, though it's been awhile for me tbh) airports. For those without, well the process is a PITA.. shoes off, gels out, laptops etc. most of us have been there - specially those who can;t get Pre Check.
Recently I experienced very long lines at SYD Int and LAX TBIT for international flights. the LAX line was fare more unpleasant due to the aboe.
Anyway as for why many (more) around the world are packing more into carry on and trying to get away with it (as opposed t the Ryan types from Up In The Air who have it down pat) it's simple.. as pointed out earlier.. same reason air tags have gone bunta.
Lack. Of. Trust.
Now the FF's do it more to be off the plan and on their way without waiting. This has been a thing for years (how old is that movie? 2010? no 2009. I was close). But now most people hear the horror stories and think oh no. I don't want my bag lost and all so I'll do carry on.
The reality is probably the chances of actual lost bags are only slightly higher overall than they used to be, but it's out in the wild so people want to avoid that chance and so... carry on it is.
Plus you have issues like the bag throwing video and the like ADDING to the poor trust issues for checked bags....
Recent trips I was on for a few weeks with a bunch of flights had no bag issues, which is what you'd expect as the norm but I'd be lying if I said I didn't check the AA app (for example) to check the bag was scanned on the aircraft
so you have more people doing bigger and more carry on items out of mistrust/fear, with related delays caused by space issues, and people not using seat in front of them for primary storage too (I get it.. we want legroom!)
in trying to avoid one potential issue, others follow.
So, we need a change of attitude (ie: trust to be re-earned - which is so much harder when lost. So this means correctly delivering bags in a timely manner) combined with better policing of the obviously way too much carry on items to try and change behaviours
this also requires consistency. Something some organisations are not terribly good at
imo.