Because of the rubbish they teach
I work in schools, I'm a school IT manager and I've been in a different school every year since I left uni, on average. Common amongst them all is that none of them know how to teach IT. This stretches from primary (4-5 +) up to college-age (18) - SAT's, GCSE's, A-levels.
IT apparently includes:
-Formatting text in Word.
- Playing with LEGO MIndstorms and 2-3 line programs using them.
- Programming in LOGO (nothing wrong with that, but we're talking about Prep School 10-year-olds, maybe a handful of hours a year in ONE year, or state-school 15-year olds doing the same).
- Going on Google Images and copy/pasting anything you like the look of into your document/slideshow.
- Knocking up a two-paragraph web-page in HTML (and using possibly the ugliest, improperly tagged, out-of-date, standards-incompliant HTML you've ever seen in your life).
- never ever once touching a REAL programming language (even BASIC would qualify - most use some proprietary "graphical" languages that's just a flow-chart in a GUI).
- never ever once being able to correctly label parts of a machine (base unit = hard drive is scarily common amongst educational posters, teachers, etc.)
- never ever once learning how a damn computer works ("It's all done with 1's and 0's... okay, next subject... batch processing...")
- teaches outdated junk like bank's "batch processing" overnight - give three reasons why. DULL, DULL, DULL, and the kids are led to believe that it's "advanced".
Modern curricula are basically what-the-secretary-thought-her-daughter-must-know. It's a list of things like "describe the function of anti-virus software", "describe which program would be more suited to writing a book".
By A-level, kids SHOULD be doing TCP/IP or some variant, binary arithmetic, coding in C/Java at least, building Arduino's and other embedded projects. I know I was when I was their age and that was with no formal education, and my degree is actually in Mathematics first. Instead, at age 18 they're still doing things like explaining dragging-dropping and telling people what WIMP stands for.
Educational IT courses are a complete, utter, 100% waste of time. I've yet to see a single IT teacher who I would confidently trust to update Flash on their laptop without breaking something. I've not met ANYONE teaching it that I would trust to open their computer and insert a PCI card, or to write a 2-line shell script. Hell, anything command-line scares the bejeezus out of the teachers I know.
Point, click, copy what I did, next subject. We're going to breed a generation of people dependent on machines who have NO idea how they work.