To hype the movie and keep blurring the line, Columbia Pictures sent Dewey and his Hard Walkers band on a seven-city “Cox Across America” concert tour that even had them performing at Cleveland's Rock and Roll Hall of Fame. The studio-orchestrated Dewey drumbeat started days earlier – those who joined his online fan club received souvenir pairs of his “tighty whitey” underwear signed “I Love You” on the rear.
Reilly also performed a slightly tailored version of the titular song "Block Hard," instead of "Walk Hard) on Monday Night Football.
In Reilly's case, he probably a) believes in the project, but also b) knows that this is his first major stab at a leading role. He likely needs it to open big to prove to studios that he can carry a movie.
But, Reilly's toil is not unique. It is more common to see actors go on whirlwind publicity tours, glad handling in China and Russia (and the UK, even if it means getting hit with a squirt gun). My guess is that with more of the mega-stars getting a percentage of the take; they've become more willing to do the time-consuming things required to get the audience. In a word, incentives.