Why government tenders requires so many documents while Private company's tender never require so much?

To increase the Competitive environment and to avoid any kind of integrity issues which would spoil the government name.So such scrutiny required through documentation.

Government tenders require more scrutiny and thorough due diligence due to the fact that they are funded by taxpayers' money. Moreover, a politician's nightmare is to get caught mismanaging public funds. Therefore, it all boils down to keeping constituents happy and not losing the next election. 

Policies and procedures of private companies are flexible and they are able to standardize the documentation according to the project requirements.  For Govt companies they have to just follow tender and procurement procedures and not able to standardize or change any item for a particular project.