Maybe for their first wave they prefer vehicles directly in water so they can use their guns for support fire - being inside LCAC blocks the range of fire they can direct. So LCAC is used for troop transport instead. But that doesn't mean they can't use it to transport vehicle for successive waves.
Well if that is the case it would be a first
Because if you need to soften targets up on the beech as you approach it means that beechhead is not as secure as you would like and sending in a trooped filled LCAC would mean nothing but very heavy bloodshed, I mean you could easily have 70 troops on that LCAC and a direct hit would be very disastrous I would not like to imagine
Whole point of a LCAC is it's speed and ability to go from water to land quickly while lifting armour not troops or marines
The beech would be softened up by attack helos and bulk of marines would arrive on transport helos and also with the land forces
The first punch on a amphibious invasion from the sea is to land heavy armour like the IFV or even better a MBT and secure a zone to land more equipment I do not know if slow moving IFV and infantry could do that without a dedicated use of LCAC which has the range of say 15-20km from the mother ship something the slow swimming IFV just can't do plus LCAC means a over the horizon landing probably a pre request nowadays in a amphibious invasion
Type 071 emerged what 7 years ago and Type 726 has seen only 3 units with two known commissioned even been on a anti piracy mission we have seen it carry tanks and IFV but never in a fully blown excercise, that's fishy just doesn't make sense