A continued Republican electoral college advantage (which doesn't exist by the way) while losing the popular vote would actually hurt the Republican Party by creating weakened Presidencies like the Trump Administration. The Trump Administration is already so weak becausr of the popular vote loss. And that loss has shown Congress how weak the president is.
So it's not actually in the Republican Party's interests to solely focus on the electoral college. They need a President who can command 55% of the country and create a broad mandate.
Yes, eventually the situation won't hold because weak incompetent presidents like Bush and Trump will turn ever more young voters against the Republican Party. Also, long-term, more and more states will sign on to the NPVIC.