Whoa, that chart seems really misleading. There are 3x more CS majors than math majors and 2x more than physics. The chart is showing derivatives, not absolutes. That basically undermines the title of the article. Looking at the graph, it's also super important to see the context before 2005 -- that start date adds significantly to the misleading impression this graph is giving. Math had more majors in 1970 than it d…
I'm not very surprised by that: not very many people are smart enough to do math or physics, while computer science is much easier.
Meanwhile, the fields that are larger than CS are the engineering and biomedical ones. I feel this is a bit vulnerable to how you slice it though, e.g. the number of CS graduates are presumably more numerous than any particular type of engineering (mechanical engineering etc). It's a bit of an accident that all those fields are grouped together and computer science is not. (This could have been otherwise, e.g. in Sweden you can study both of an MEng in "software engineering" or a BA in computer science, and the content is quite similar.)