truckandbus: only 30% of engineering grads in Canada work as engineers, so that 1/2 of the students you interview who don't want to be engineers are in good company.
However, your anecdotal observation of the students you interview runs contrary to the measurements. Our local engineering regulator PEO has been surveying substantial numbers of 4th year engineering students each year for quite a few years, and the results are consistent: over 90% of the graduates will either definitely or probably seek a career in engineering. Only about 6-10% know in 4th year that they are going to pursue something else, i.e. medicine, law etc. So that leaves about 60% of the graduating class, ending up doing something else by default, not by choice. And after a few years out of engineering, they're considered "spoiled" and not suitable for re-use. They've lost their profession for good.
Why do so many fail to gain entrance to the profession? Too few employers are willing to take them on and train them. They expect to find people with 10 yrs of relevant experience gained elsewhere, who can hit the ground running. That only works a) during recessions or b) if you offer significant salary premium. People who build their businesses on that kind of growth model SHOULD find themselves with a shortage of candidates in my opinion- they're shortchanging not only themselves, but the whole profession.