OK, it's the law itself.
Blaming Republicans or the insurance companies can only go so far. First of all, the administration wrote the rules that set the conditions under which plans lose their grandfather status. But more important, the law has an effective date so far in the past that it virtually guaranteed that the vast majority of people currently in the individual market would end up with a notice saying they needed to buy insurance on the Obamacare exchanges.
Any effort to pin the blame on others is a classic case of misdirection. The vast majority of the problem stems from the effective date, which was imposed by the administration. Given the problems which stem from it, it is easy to see why loyalists must attempt to keep the focus elsewhere.