It's been a trend with them since Americana. "Pretty Fly" and "Why Don't You Get A Job" were two tongue and cheek songs that they released and they ended blowing up as huge hits. But the rest of that album didn't sound anything like those two songs. They have continued that formula ever since. I guess in an attempt to get another huge pop radio hit. It's sad because by releasing songs like that they tend to give people the wrong idea or impression of the band and what the album is going to sound like as a whole. The good thing about it is they have always kept their aggressive punk side too and the good seems to always outweigh the bad and I'm happy to say that's definitely the case once again with this album.
Or they know that tons of people listen to their band because
of "Pretty Fly" and "Why Don't You Get a Job" and they want to make everyone happy so they include goofy pop songs on all their albums.
Or maybe they themselves just like goofy pop songs...