if you aren't willing to pay them more. Many more people will choose to become teachers if they can at least have the chance at eventually getting to upper-middle class in income level. It is as simple as that.
I do not dispute that there are many problems with the current system, and I think that a revolution in how teachers are evaluated and compensated before a massive shift in pay should happen, but that does not change the fact that the only way to attract the best and the brightest would be to pay people more.