Until 2017 it took 60 Senate votes to confirm a justice. In order to be confirmed, nominees had to have moderate enough views to get 60 senators to vote yes. Senate Majority Leader Mitch McConnell changed that rule so now only 51 votes are needed.
The last Democratic Majority Leader did the same thing for lower court judges because Republicans blocked most Democratic nominees.
Since McConnell’s rule change, Justices Gorsuch and Kavanaugh were confirmed with fewer than 60 votes.