Robert Novak said, "God put the Republican Party on earth to cut taxes. If they don’t do that, they have no useful function." Since they were also put on earth to repeal Obamacare, and failed to fulfill that divinely-appointed role, they must enact fundamental tax reform if they want to maintain their majorities.
We have had Obamacare since 2010, and we have not had major tax reform since 1986. Doing anything on Obamacare through reconciliation, which only requires 51 Senate votes, is off the table. That ship has sailed.