It’s because the liberal fascist party, ie. the Democrats, constantly call them conservatives.
This despite the fact that most of the so-called “moderate” Republicans are more liberal than JFK Democrats back in the day, and the RINOs themselves would melt invisibly into the party of LBJ.
But the Democrats and their hack propaganda media have been calling them conservatives for so long they’ve actually come to believe that’s what they are.
The truth is, they are conservative – but only in comparison to Lenin, Marx, Stalin, Mao, and Pol Pot.