On the one hand, yes, you have unions, which theoretically are sticking up for the workers but in practice spend a large % of their time and resources sticking up for the lousy workers who deserve to be fired anyways.
On the other hand, you have about half of the country devoted to relentlessly slashing education budgets in the name of "less government". In a small-l labor dominated industry, that effectively means smaller paychecks and/or more work for the same pay. So good teachers who are frustrated by the union shenanigans don't have a lot of other alternatives - who else is gonna stick up for them?
Real solutions would be a combination of big pay incentives for star teachers (not that I'd necessarily be a star, but why on earth would I teach at those rates when I can be an engineer?), coupled with a much looser structure on tenure, more dynamic general situation, etc. That would be the kind of incentive to empower the good teachers and disempower the bad ones. But you can't just blame the unions without addressing the other side of the coin.