Can see what you mean, and it adds failure points. However a small leak which starts after your initial bubble check could go unnoticed (especially if close to an o/c diver). On the other hand the leak is quite likely to be from the hose/guage!
The other thing is that if using one cylinder of O2 for several dives I feel more comfortable knowing I still have enough left
Doing drills I haven't felt the volume of the hose caused a big problem. I suppose narrower bore hoses or a pressure transducer on the 1st stage and a remote readout would be possibilities if it is a problem.
Neil