For one, there’s no guarantee that insurance companies will continue to participate in Obamacare over the next several years knowing that the law is going to be repealed.
Over the first few years of Obamacare’s implementation, insurers have lost billions of dollars trying to sell insurance through Obamacare. Many of them are willing to stick it out, for now, in hopes that they could establish a foothold in the young market and be in a position to profit if and when it stabilizes. But that calculation changes dramatically if they know that after several more years of racking up losses, the market is going to expire anyway. Many more insurers are likely to exit ahead of the 2018 year, disrupting people’s insurance arrangements.
Additionally, the political landscape could change dramatically between now, when Trump and congressional Republicans have just come off a huge election victory, and the 2018 midterms, when the party in power historically suffers setbacks. President Obama came into office with much stronger political standing in 2009 than President-elect Trump will, and within two years, he had completely lost his ability to achieve any of his domestic policy goals.