H1B is basically how big companies remain 'leen' enough to compete with start-up. This is made very clear in Amazon and PayPal India offices afaik, but sounds reasonable enough to be generalized. It is impossible for a large company with thousands of employees to remain competitive without the crunch-culture of startups. So they get H1Bs.

What are the penalties for trying to leave it? I think that that's the defining factor, for what we're talking about here.

When equity is being traded for a reasonable salary, you lose your lottery ticket. It may not be as big of a carrot, but it's a carrot nonetheless.