Never been in such a situation, though I can imagine:
- Remaining cabin luggage is "offloaded" by low-paid workers.
- This stuff is brought "somewhere", where the authorities will scrutinize its contents.
- The stuff is relocated to a location to be united with the passengers, still being around.
- Passengers will need to identify which items are theirs, either verbally or by pointing.
- Of course, when collection/returns are done rigorously, there will be some cross-references with allocated seat and location retrieved (read: time-consuming).

So, yeah, quite some moments when those in need of nice things or money, can grab their chance to have a free shopping opportunity.
Not to say, all those luggage items that don't have suitable identifying marks will be a challenge to get that back.

And this whole process will of course take a huge amount of time.

So, yeah, there are pretty valid reasons passengers don't want to be separated from their valuables/possessions.

Note: Many people having emergency vacated aircraft "with" hand luggage afterward reported, it was not theirs, though they took it with them, because it blocked the evacuation. So (maybe even by far) not everybody seen evacuating with hand luggage is saving their own stuff......

I really doubt that. Checked bags are retrieved and put onto a carousel for passengers to collect on every single flight, yet the #1 concern that passengers have about checking luggage is not theft by employees or other passengers, but rather the airline losing their luggage (which is almost always returned to them within a few days).

If someone else's carry-on is in the way during evacuation, I fail to see how bringing it with you down the slide is going to help. That takes far more effort than just stepping over it inside the plane.

CX 880 is starting to be a cursed flight number -- another major issue delayed this flight for 12h:
Hong Kong authorities order Cathay Pacific to investigate leaking aircraft water tank that delayed Los Angeles flight by 12 hours | South China Morning Post (scmp.com)

Hong Kong authorities order Cathay Pacific to investigate leaking aircraft water tank that delayed Los Angeles flight by 12 hours

• Flight 880 delayed because of leaks found while servicing one of aircraft’s water tanks, Cathay says
• On Saturday, Los Angeles-bound flight aborted its take-off in Hong Kong and abruptly braked, with 11 passengers hurt while using emergency slides

It's not about checked luggage, but precious cabin luggage, with passengers' valuable belongings.

Well, I did read first-hand reports about this, that people were confronted with cabin luggage blocking the aisles, etc, and just bringing that cabin luggage out of the aircraft, to avoid further evacuation hindering.

Or so to say, the perfect example, the China government's authoritarian way of the ruling has entered the Hong Kong government organizations.

"Authorities order to investigate" is not something seen in Western democracies.

Makes life "easy" for these organizations, until it becomes clear, this is a downward spiral of power enforcement. And then things start to become more and more difficult and more draconian enforcements are needed to stay in control, etc.