When most Republicans voted to pass the Budget about 10 months ago, they agreed to a two year extension on bailing out any health insurance company that lost money on ObamaCare policies.
Just three months before that Congressional vote, during the 2014 election campaign, the same Republicans were telling their constituents that a Republican Congress would REPEAL ObamaCare!
Oh, and United Healthcare is bailing out of O-Care one year BEFORE the subsidies stop!
Crocodile Tears Over The Failing Obamacare Co-Ops--The Canaries In The Obamacare Coal Mine
The biggest complaint seems to be that those mean Republicans forced these co-ops out of business because of a provision they included in the last budget. That provision capped what could be spent on the Obamacare risk corridor reinsurance provision for health plans losing money at the level of what was paid into the program by health plans making money. In other words, the Congress reminded the co-ops and the administration of something that was assumed all along - that the risk corridor provision had to be revenue neutral.
The specific complaint is that because of this Republican budget cap health plans got only 12.6% of what they asked for and expected to get under the risk corridor reinsurance program.
If you would like specific info as to why Obamacare is collapsing & United is bailing, here it is (more excellent info/reading):