I find that the people that are best at research (and thus most likely to get tenure) are usually very poor teachers. Usually they are so good at their subject

I find that the people that are best at research (and thus most likely to get tenure) are usually very poor teachers. Usually they are so good at their subject that they tend to skip steps in their explanations and forget how difficult a certain concept is and expect everyone to breeze through it. Unfortunately, universities optimize for research rather than teaching.