The engineers are not getting that obviously, it depends on how much equity they have and the difference between the amount of VC money pumped into a company and the final sale price of the company. VCs often get 2x preferred stock (at the minimum - it entitles them to 2x what they invested). This is before anyone else is allowed to see a dime. Every term sheet is different of course.
The value of the team is also larger than the individual engineers on it. Plus, a package bid is less risky if you're looking to get the entire package.
Oh, and poaching has another risk - that you get only the worst employees.
To put it another way: if you personally promised the engineer $5 million (vesting over 3 years) they may switch.
This means the buyer must see some value in the company over and above the engineers. (IP? Customers?)