I think it comes down to two issues, the first probably being the more significant:
1. My impression is that most training these days is more spread about (e.g. up to 1 lesson per week depending on weather), whereas the majority of those 'good old days' figures you see someone was doing an intensive course. During my training I certainly noticed that if I hadn't flown for a couple of weeks due to weather cancellations or whatever, I spent a reasonable chunk of the lesson just getting back to where I was at the end of the last one...
2. When it gets to circuit training, some of the larger circuits flown these days (e.g. due to noise abatement, or sadly more frequently just due to instructors teaching bomber circuits for no apparent reason) can lead to getting fewer circuits done in the same time. Given that after the first few, the majority of the circuit isn't teaching anything new (i.e. the important bits are to a lesser extent the climb out, and primarily the approach and landing - crosswind / downwind get mastered fairly early), if it's flown wider and therefore longer it can take a lot more flight time to do the same number of approaches / landings...