The plot of Super Mario Bros. is essentially the tale of one long real estate struggle, as Bowser attempts to take over the Mushroom Kingdom and Mario shows up way too late to prevent him from doing so. Despite forming the kingdom's entire defense force, Mario rarely hears about an invasion until after Bowser has had enough time to build a series of castles. Archaeologists have responded to invasions faster. At a certain point, Mario has to feel less like a hero than a Rascal Scooter -- prolonging the lives of thousands of terminally mushy creatures who would have been no match for evolution if left to their own devices.
"At least Bowser makes the trains run on time."
While Mario is always in crisis mode, Bowser's motives seem to oscillate between good old-fashioned land lust and not having anything better to do on a Sunday. One of the few times Mario arrives early enough to see Bowser make off with the Princess (Super Mario Galaxy 2) was when it was such an incredibly minor part of the plan, Bowser was clearly doing it just to piss Mario off. And when you can mount a planetary assault just to shout "Screw You!," you're winning so hard the scoreboard turns into a diamond.