It is hard to hire good anyone because reality has a surprising amount of detail: http://johnsalvatier.org/blog/2017/reality-has-a-surprising-... and many if not most people are poorly suited to abstract symbolic manipulation work.

Add to that the difficulty of the profession itself and the constellation of ancillary skills one needs (conscientiousness, the ability to interact with other people, articulateness, the ability to disagree respectfully and intelligently, etc.) and you will find it hard to hire good "x" in general.

Finally, it is often hard to hire good "x" unless you are paying at or above the market wage for x. The people who have a hard time hiring are generally not paying the market wage or above it. When they do, they suddenly find it much easier to hire.