The only reason millions of Republicans voted for Trump was because they were terrified of having someone not-conservative in Scalia's seat. It's the only reason Trump's president. Imagine the absolute uproar there would be if President Kamala Harris added two more seats. The Democrats would lose every election for the rest of the first half of the 21st century. It would confirm every (currently) unfounded suspicion Republicans have about Democrats.
There were two forces at work in Trump's 2016 win. Yes, millions of Republicans held their noses or blocked out their brains and voted for Trump because they cared about the Supreme Court. But Trump got the same number of votes Romney and McCain got, and some of those were "new" voters for Republicans, so he surely lost a lot of Republicans in spite of the open seat. The other force at work was Dem apathy about Clinton or complacency she would win which kept millions of Dems at home or voting for third party candidates.
You can have every Republican excited about the Court showing up at the polls, and they're still only one part of the equation. If Dems show up, Republicans get outvoted.