Using stock as collateral for loans with insanely low interest rates is very, very common among even engineers in big tech. It’s a well known loophole passed on by the older engineers/managers at the companies to the younger ones. From the perspective of eventually paying the tax it doesn’t help, but inflation will outpace the interest on one of these loans so it does lower the effective rate and more importantly for the economy as a whole is cash earned/spent without having been taxed. Ya it will need to be paid back eventually, but that can take decades.