There is a very simple & honest answer for unrealistic requirement, one word: "no".
A contractor who's afraid to say "no" is to blame when his efforts fail.
The government should be in the business of putting such contractors out of business and raising up others with the courage to say "yes" when they mean "yes" and "no" when they mean anything else.
Believe me, it's all about the very most basic of basics.
If you're mind is screwed up there, then nothing will ever go right.
You have a simplified answer for a problem you don’t have experience with.
There are many cases where contractors say no. When a company thinks it can not make a profit on a contract, it can and often does “no bid”. If the contractor tells the customer that they can do it for X price, and the customer agrees, and then the customer comes back after contract award and says “ we want you to change A, B and C to meet additional requirements we forgot to tell you about” then cost will increase.
You are in the meme of blaming the contractor. Why don’t you talk to Trump about how contracts works. You don’t ever get anything for free. If you want “better”, then it will have a cost above “good enough”.