My understanding for an ENT conduit (other than for future flexibility) was that it was fire-rated, to reduce the spread of fire/air-flow between floors. If the conduit went through fire-blocks or floors, holes would have to be sealed with fire-retardant sealant/caulking.
Note the low-voltage backless gang boxes.
Doesn't the backless gang box defeat the purpose of fire blocking? If a fire starts in that section, it has no obstruction to enter the ENT conduit (through the backless gang box) and go all the way wherever the conduit leads to? What was the point of sealing off the floor/fire-block hole then?