The money to be made by getting it once and doing nothing will always exceed the income you could make by maybe doing it well enough to get the future contract.  And be less than the money you can get by taking the contract, doing nothing, and BRIBING your way into the future contract (even after subtracting the bribe).
Private business is no less prone to corruption than government - ESPECIALLY when dealing WITH government.

A few years ago I worked for Oracle corporation - one of the largest software companies on earth. While I was there, Oracle (not my division) got the contract to develop the Obamacare exchange for the US state of Oregon. They received a 50% upfront payment of over 60-million US dollars. The delivered ... well basically a website you could do in a weekend for 1000 dollars. 
They didn't get the other 50%. They didn't care. They will never work for Oregon again. They didn't care. They are being sued. They didn't care (lawsuits take decades).

I resigned in protest.