Regarding costs - yeah, it's important to have the funds to be able to finish training. But a lot of people forget that you need to have money left over when you get that ticket so you can do the flying you were training for.
There is twice the amount of money left over to go play if you get the checkride done at 40 hours instead of 80.
IMO just guessing: The FAA probably isn't the driving factor in the hours increase over the last couple decades. There has been stuff added over the years but not THAT much stuff.
Some potential ideas of the cause:
Instructors nitpicking or dragging out time or just not having the teaching skills maybe? I watched an instructor freak out about a STOL 172 approach when I said what I was going to do and slowed to 55kts on final when 45kts would have been safe. 65kts is minimal or certain death will occur especially at higher runway altitudes - or so I was told on downwind after the aborted landing. On the other side of that, I had an excellent instructor who knew how to teach and understood flight. My very first x-wind landings were in a left 10kt direct x-wind. The ground lesson to make it a non-event was about 5 minutes with two pieces of paper, a pencil, no writing and a simple comment about what effect the rudder and ailerons have on the air mass in relation to the ground motion - total clarity of the situation because the explanation made sense.
Students not taking it seriously maybe? An hour every two weeks? Not doing their homework? Coming to the lesson unprepared? Learning because it's a side hobby that is done half heartedly? The written is not a PhD level exam. Study, understand, take practice exams, understand the wrong answers, take the written and be done with it. Think about your average 3 hour college course - that's all you need to do for the written.
Maybe it's cultural nowadays. Look at what people do. Instant gratification. Nitpicking irrelevant details. (Calculations to the nearest 0.0001 gallon or 0.01 degree is not necessary to solo or even for a PP checkride) Overfocus on one thing while ignoring all the other things going on resulting in a complete lack of focus on the total environment. Not wanting to put the effort into something. More wishy washy teaching methods. Lack of concentration. Wanting the end result without the effort of the paperwork or understanding. Minimal standards being completely acceptable and studying for the exam only.
I think the worst is people saying they want to do something but their heart isn't really into it. I see college theatre students of all ages that say "I want to try" or "I want to do" with no conviction behind it - and those individuals get the basics however they turn out to not really be any good at what they end up doing. It's the ones who put the extra effort into it because it's who they are that are the best.
Flying is way too dangerous and demanding to not be dedicated to the learning process and effort required. Is the desire to fly an internal Want or an internal need Need? You either need to fly or you don't.
Just something to think about.