Well for starters it wasn't purchased by or for schools so no. But even if it was, it gets far more than 3 years of support. I think 5 is somewhat reasonable if we're just going to accept this sort of behavior.
Either way the comparison is not really apt. Mobile devices are far worse about this than PC's. You should instead compare a macbook (or a cheap windows machine), which gets security updates for 7-10 years. Google knows their devices are very popular for school computers, so to treat them like mobile devices and enforce the terrible standards that comes with is pernicious.