The headline "startup bought for x million" is almost always a lie, either direct or by omission.
First, when a startup is bought, its generally not bought at the headline rate. So if you see a "bought for $45m" that doesn't mean People who own shares all got a % of 45m.
That number is normally bullshit, but also a "total package" which include share offers for joining the new company.
This means you will get say 1% of the headline buyout now, and then golden handcuffs to get the rest.
Also, it makes no sense to give employees that much money upfront. After all, if I'd been given $1m in one go, I wouldn't be fucking working now.