Piper Classique makes some very good points about the training environment and the required knowledge but his best observation is that students move into the circuit too soon.
Monocock has also identified some very important factors, his first and last bullet points being particularly astute.
Having got out of the standard flying club loop and moved to a non profit club I find that we don't have the problem with bad instructors ( because it is not a place to go to get hours for an airline job ) or being driven to push a student into parting with money add to this a circuit that is very tight by today's standards and you have all the pieces of the jigsaw needed for speedy student advancement.
I have said before on this forum I think time to solo has more to do with the number of landings a student performs, not the number of flying hours.