This article hits the nail on the head. The basic structure of Obamacare was put together by the conservative Heritage "think tank". Mitt Romney passed a bill based on that structure when he was the governor of Massachusetts. Its been hard for Republicans to find an alternative to a conservative health care plan that has enabled millions of low income Americans to purchase health insurance in a market subsidized by the government. The next question that a thinking person might ask is why do Republicans want to repeal Obamacare? The answer is not difficult to find by those who understand Obamacare. In the first place, Republicans can't support any plan called Obamacare. It was OK when it when was called Romney Care but Republicans did not want Democrats to get credit for extending healthcare to millions of Americans. They decided to turn it into a weapon against Democrats by naming it after a president that millions of Republicans were taught to dislike for a variety of reasons. After all, Obama was not really an American.
The next major reason why Republican's want to repeal Obamacare is that it contains a very progressive tax that provides funding for subsidies and other incentives that make it affordable for low income Americans. Each of the replacement plans proposed by Republicans eliminate the tax on Americans with very high incomes. Consequently, any replacement plan must reduce the benefits for low income Americans because of the lost tax revenues. Republicans in competitive districts don't want to run for reelection after voting for a plan the Democrats will use against them. The Freedom Caucus Republicans are another matter. They represent conservative districts that would rather shrink government in the cause of liberty.