Most engineering internships at this point are paid and most people on HN are working for companies that do paid internships. Unpaid internships tend to be more prevalent in the arts and at small companies. Anecdotally I distinctly remember people doing design for free as interns, with very little oversight or training. Back in the day Craigslist would have a number of these types of "internships" although I think these are no longer common due to both better enforcement of laws and more importantly the rise of the gig economy creating competition