The GOP would be motivated to clean house if there were some push to do so from the saner elements of their base. If it were obvious to them that doing so would cost them elections. That isn't happening. The pressure is coming from the Democrats and the left-leaning media, in other words, the people who wouldn't vote for them anyway. Their own base consists of extremists and moderate cowards who whisper about Bush and Reagan but don't dare say anything against Trump out loud.
McConnell will do nothing because he has nothing to actually gain by it and will lose nothing if he doesn't.