The government procurement process is insanely complex. A full competitive bid process for something of this magnitude would have taken many months at least, and would also make it really hard for consortiums to bid because of the up-front cost. Hence the beltway incumbents (Lockheed, Northrop, IBM, and, yes, CGI though they're much smaller) have a much easier time winning these contracts since knowing how to navigate the contracting process and having existing contract vehicles unfortunately gets you a large part of the way there.

I believe CGI actually got this contract via an IDIQ, which is an "indefinite delivery/indefinite quantity" contract, allowing HHS to add additional "tasks" to the IDIQ contract as long as its within certain bounds set by the contract, and if it stays within their GSA fee schedule. IDIQs started becoming popular in the 90s as a more expedient way to contract rather than the months-long or even years-long process of a standard competitive bidding process. However, it only really solved the procurement woes for incumbents. I couldn't find the original CGI-Federal contract, but here's at least their press release: http://www.cgi.com/en/CGI-selected-build-US-wide-competitive...

Also, here's Accenture RFP award as the prime for fixing up the site for the next enrollment cycle. https://www.fbo.gov/index?s=opportunity&mode=form&tab=core&i...