It's almost like movie studios want to make money in this multi million dollar industry and charismatic screen presences make for popular casting choices due to familiarity with the common audience. Put two white hot people in a movie together and people will see it even if it sucks like Passengers (that'd be the Pratt/Lawrence disaster) which was the second highest grossing original live-action film of that year. 

Viewers have enjoyed popcorn entertainment for years and it's only going to be that way until the formula breaks.