Because it is expected that A, traffic would obey the road signals
In this case, it looks as though the driver obeyed the signals/lights. Just that they may not have complied with signage requiring slow moving vehicles to contact the signaller (if indeed this was present and clearly visible).
B, traffic would be going in the right direction
It's unclear whether the lorry could have squeezed through half of the road, if they'd been going on the correct side of the road.
C, if a car or lorry would happen to get caught they would stop and not rip the barrier off be continuing on
Most drivers would, quite reasonably, consider they're better off breaking barriers than getting stuck on a crossing. In any case the barrier only started moving just before the cab passed the barrier, so with reaction time it's unlikely the driver could have stopped in time to stop it colliding with the cab.
Its there to check the crossing is clear before clearing the signals.
Indeed. Which means that NR's claim that the lorry driver was "endangering passengers and trains" is utter nonsense. Unless they're suggesting there's a risk if the signaller doesn't do their job properly?
As I said, it's no good considering level crossings from the idealistic perspective of "people will stop when the lights are illuminated and comply with all instructions, no matter how complex". That's asking for trouble.
You have to have a holistic view, in the same way as multi-SPAD signals are sometimes fitted with countdown and warning boards. And how TPWS is fitted despite it being unnecessary in an ideal world.