When I was an FA, not only was initial training very intense, but you didn't get paid for it *unless you successfully completed it*. I've heard from some current FAs that their airlines don't even pay their room and board during initial training anymore.
Now, you may ask, why would a person want to put themselves through such crazy training for no pay, and for very little reward afterward?
It can be best summed up by this little scene that occurred on the first day of training for me. We all walked into our training class and sat down. There was a woman on the floor, nicely dressed in high heels, stockings, skirt-suit, but knees on the ground, rear-end to us, searching frantically for something. After a few minutes, someone piped up: "Can we help you find something?"
"I'm looking for the glamour in the job. I haven't found any in 15 years, but I'll keep looking."
It's not a glamourous job. It's not "fun". It's work. And no matter what propaganda the FA's try to spew down your throats, no, a flight attendant's job is not for the health and wellbeing of the passengers (nor are you a waitress in the sky). Yes, we were trained for that, but it's more a Customer Service position - you need to be able to keep people happy and calm, by whatever means at your disposal, because you're entirely on your own up there. It takes a special kind of training (and people) to think and act quickly and independently, without the need for external management.
And - to be able to adapt to an ever changing work environment. Your team rotates on a constant basis. Who you fly with today won't necessarily be on your crew tomorrow, so you need to be able to trust their training and their abilities.
So, the pay sucks, but the training is invaluable.