Perhaps one reason is that job-hopping is very common in the tech industry. I wouldn't expect many apprentices to hang around long enough for there to be a payoff to the employer.
That said, my org supports up to 4 concurrent interns (typically we have 2-3 at any given point), and they could work for 4 months to 2+ years if they want, 15-40 hours/week -- adjustable for summers, etc... But they need to be at a stage where code review is going over application of theory, not telling them about when to use functions.
We lose a lot of interns after 3-5 months, but if they came in knowing the basics, we usually get something out of it (though the cost-benefit is usually negative). We want to support internships, though, so we keep doing them.
Where with clerical tasks you can just have them get back to that pile of paper tomrorrow
You could say the same thing about a professional taking an apprentice in any trade ... and yet they still take apprentices