Equity is basically always monopoly, you generally can't even evaluate its value because no one will show you the cap table. Highly profitable startups still regularly manage to deliver a pittance to early employees on exit. Even if the exit does deliver oftentimes the yearly compensations disparity is so large that if they'd just stayed at BigCo and invested the bulk of their earnings they would have earned as much or more. This is all while working significantly more hours per year.
The list of upsides is really small relative to the risk. If startups want talent the industry norms are going to have to change.
Not showing the relevant details of the cap table is ridiculous, companies that do this are banking on a pool of candidates that are either morons or don't care what they're paid.
Imagine the following situation: You're in a foreign market, and a vendor tries to sell you a fancy-looking machine. You know he's legally bound not to lie, so you ask what the machine is worth. He says "it's worth 2 billion Magic Moneys!!" but refuses to give you any information that would help you suss out whether that's 20 cents or 20 million dollars.