Oh, I don't know, maybe Nixon bugging his political opponents and starting the realpolitik BS that Reagan continued, such as bombing Cambodia (causing the rise of Pol Pot) might have something to do with it.
Reagan was ineffectual in office. What did he do? He's remembered chiefly for appointing Volcker to the Federal Reserve, and deregulating major industries including, most famously, the railroads and airlines.
...which were actually all done by Carter. But they're things right-wingers support, so Reagan gets remembered for them, while Carter is boo, and worst president ever, and so on. Reagan himself didn't really do anything beyond continue Nixon's insane foreign policies. But he took credit when Carter's reforms started to help the economy.
Reagan's worshipers also give him credit for Gorbachev's dismantling of Soviet Communism. I'm struggling to think of a thing he's been given credit for he can call his own. Maybe cheesy folksy sales patter, later used to such great affect by Bush Jr?
It's easy to think of Reagan as a more substantial President than he really was, purely because of the hero worship the right gives Mr Gun Control And Deficits Don't Matter. Don't make that mistake. He was an ineffectual imbecile, held up in hindsight due to events he had little part in.