It really doesn't. k's ancestors were taught to high school students and admin in incredibly short spans of time. Here's an anecdote from Kenneth Iverson about a man who learned APL in two weeks, completely alone, and the results after he taught his students it:

My daughter Janet attended Swarthmore High School, and recommended Rudy Amann (head of the math department) as an excellent teacher. I therefore approached him with a proposal that we put an APL terminal in his school as a tool for teaching mathematics, suggesting that he first spend the summer with the APL group to assess the matter.

Rudy responded that he could spend only two weeks, which he did. I gave him an office with a terminal (and the Calculus text in APL that I had written after our earlier experiment with high school teachers), and invited him to come to me or anyone in the group with questions. Since he never stirred from his office, I despaired, but at the end of the two weeks he announced that he wished to go ahead with the project.

Rudy was pleased with the results, and told me of canvassing those of his students who went on to college, finding that they were pleased with the preparation he had given them. One thing he had done was to use some of the final two “review” weeks to show them the translation from things like +/ to the sigma notation they would encounter in college.

Here's another where they taught it to high school teachers, with a direct explanation as to how students responded:

I believed that APL could be used in teaching, and Adin said that to test the point we must take a text used in the State school system, and try to teach the material in it. He further proposed that we invite active high school teachers.

We hired six for the summer, with the plan that two (nuns from a local school, who could provide a classroom in which we supplied a computer [typewriter] terminal) would do the teaching, while the other four (with a two-week head start) would write material.

To our surprise, the two teachers worked at the blackboard in their accustomed manner, except that they used a mixture of APL and conventional notation. Only when they and the class had worked out a program for some matter in the text would they call on some (eager) volunteer to use the terminal. The printed result was then examined; if it did not give the expected result, they returned to the blackboard to refine it.

There were also surprises in the writing. Although the great utility of matrices was recognized (as in a 3-by-2 to represent a triangle), there was a great reluctance to use them because the concept was considered to be too difficult.

Linda Alvord said to introduce the matrix as an outer product — an idea that the rest of us thought outrageous, until Linda pointed out that the kids already knew the idea from familiar addition and multiplication tables.

Finally, it was this interest in teaching that led us to recruit Paul Berry, after seeing his Pretending to Have (or to Be) a Computer as a Strategy in Teaching when it appeared in Harvard Educational Review, 34 (1964), pp. 383-401.

(From KEI's delightful but sadly unfinished autobiography: https://www.jsoftware.com/papers/autobio.htm)