Basically the higher-ups have to decide what is most important; if the deadline is fixed, then the scope HAS TO BE flexible.

tl;dr; everything in a large corporation is a game of telephone where everyone is incentivized to muddle the message. So any deadline/commitment handed through multiple levels of management is really difficult to negotiate. And the more unrealistic it is, the harder it is the negotiate. Nobody wants to tell their boss that the thing they want done in 3 months will actually take 2 years.

  In the beginning, there was a plan, 
  And then came the assumptions,
  And the assumptions were without form, 
  And the plan without substance,

  And the darkness was upon the face of the workers,
  And they spoke among themselves saying,
  "It is a crock of shit and it stinks."

  And the workers went unto their Supervisors and said,
  "It is a pile of dung, and we cannot live with the smell."

  And the Supervisors went unto their Managers saying,
  "It is a container of excrement, and it is very strong, 
  Such that none may abide by it."

  And the Managers went unto their Directors saying,
  "It is a vessel of fertilizer, and none may abide by its strength."

  And the Directors spoke among themselves saying to one another,
  "It contains that which aids plants growth, and it is very strong."

  And the Directors went to the Vice Presidents saying unto them,
  "It promotes growth, and it is very powerful."

  And the Vice Presidents went to the President, saying unto him,
  "This new plan will actively promote the growth and vigor 
  Of the company With very powerful effects."

  And the President looked upon the Plan 
  And saw that it was good,
  And the Plan became Policy.

  And this, my friend, is how shit happens.

And yes, I've been a manager in a company where the phrase "managed out of the business" was used. I no longer work there.