Although doing it "to keep numbers low" doesn't seem to me to be a good reason to do it, it is generally a good idea to have some hard stuff early in a field.
The idea is that if the hard stuff comes too late, people might not find out that they aren't really suited to that field as a career until it is too late to change majors without having to take an extra year or two of college.
The intro class is too early for that, though, because CS is useful enough for other fields that many people (perhaps even a majority of people) taking intro CS don't intended to actually go into CS. Better is to put it in the first class in a field that will mostly only be taken by people who are intending to go into that field.
The best college courses I took were ones where the professor frontloaded all the hard assignments towards the first month of the semester. Every slacker dropped out, and for most of the semester we just had great discussions because everyone was doing the readings.
Just like DRM, make it a little harder to skate on by and you actually filter a lot of casual/non-serious people.
The idea is that if the hard stuff comes too late, people might not find out that they aren't really suited to that field as a career until it is too late to change majors without having to take an extra year or two of college.
The intro class is too early for that, though, because CS is useful enough for other fields that many people (perhaps even a majority of people) taking intro CS don't intended to actually go into CS. Better is to put it in the first class in a field that will mostly only be taken by people who are intending to go into that field.