What I read, and I did read this online and haven't had the time to look for primary sources so please take with a grain of salt, but worth looking into is this:

pre-existing condition check was a major risk to the insurance industry since nobody knew how much it was going to cost them. So the ACA told insurance companies we'll subsidize some of your costs until things settle down (this is different than subsidizing people's payments). However when it came time for the gov to pay, Republicans blocked most of the subsidy payments to health insurance companies (I think they only received 12% of the expected amount).

And then because insurance companies didn't get that subsidy they obviously passed the cost onto consumers. And I'm sure whatever subsidy was further promised by the Gov they could no longer rely on so they priced that risk in as well.