Because relative to business management or finance/insurance/real estate, it doesn't pay.
This is because of a high number of H-1B immigration visas issued, and foreign workers are driving wages in the tech fields down. Essentially, the H-1B workers are indentured servants for the tech industry.
This mass immigration is the least objectionable because the immigrants are skilled and usually English speaking. However, if you are an American student who studied your engineering and programming hard and played by the rules, doesn't it just annoy you that your hard work was just devalued? And they want American kids to work and study hard? When something pays less, you get less of it.
And so many native born Americans go work in business management or finance/insurance/real estate, where their English skills and cultural literacy give them a leg up on the people from India and China, which they definitely *don't* have in computer science.
In other words, what has happened with the H-1B visa is the white collar / upper class version of what happened to wages in the construction and building trades when large numbers of illegal alien day laborers showed up. Only in the latter case, it became easier for the unskilled and muscular to become welfare bums and "thugz".