Also, it's unclear that big companies would be willing to hire 100% of the people who want to work in tech. For some, working at a startup might be the best way

Also, it's unclear that big companies would be willing to hire 100% of the people who want to work in tech. For some, working at a startup might be the best way to learn and improve. Google might not blindly extend 100k+ more offers, above market rate, just to cover everyone who wants to be a programmer. So for the (likely majority of) people who can't realistically get into Google, a startup might be one of the best ways to learn and make money.