In my opinion it is a matter of economics. At currents rates of pay coupled with training costs it is a very unattractive career option. I believe that most people now go into instructing as a means of hours building. This has worked well for the employers in times of excess supply but the balance is starting to change and we are hearing the first demands to reduce the qualification requirements particularly for PPL instructors.
At the end of the day, if instructing is to become a viable career option then employers (and the end customer) will have to improve pay and contribute to training costs. My belief is that basic economic principles of supply and demand will dictate. We can therefore expect career instructing to become a viable once more.