I believe that people are abandoning Christianity because the loudest Christians today are motivated by politics and bigotry and lust for power—not anything Jesus taught.
Young people see Trump fanatics speaking for Him, not the Jesus who said love one another, turn the other cheek or preached the parable of the Good Samaritan. Because the cruel cultists have succeeded in hijacking Jesus Himself, young people are running the other way in a huge wave of rejection.