Startups are going to be like that, but you said you were interviewing at AWS. You can buy and sell their equity on the open market, so it's not really a mystery what you're getting. If they say they give you 50 shares a year, that's $137,941 a year in cash money. Probably more next year. You can sell it or hold it, but turning it into cash is very easy. Sure, Amazon could go out of business while you're holding stock grants and then you get $0... but that's exceedingly unlikely. A lot would have to go wrong for Amazon to lose all its value.

When I was new to the FAANG world I pretty much valued the stock at $0. I quickly learned that that was not correct; stock ended up being half my pay. (Probably more than half as you move further up the ladder!) The base salary is good, but another 100% on top of that was also pretty okay. I guess until you've seen it, it all seems mysterious. But I can assure it's almost as good as cash, minus whatever you pay someone to fill out all the tax forms.

As for why these companies give you stock instead of bumping up your base salary to be what you'd get by selling the stock right when it vests... apparently it's cheaper for them. It's not quite the same as printing money, but I guess it's close.