Symbolism, Imagery, Allegory
Marvin K. Mooney may not have a choice about whether or not he leaves, but he has a variety of options available to make himself sparse. Did Seuss miss any type of transportation? Brontosaurs maybe, but when you have the Zumble-Zay available, do you really care? (Maybe a little….)
So anyone who picks up the book can see there are lots of fun and playful illustrations featuring the modes of transportation. Why so much emphasis and imagery on how Marvin K. can leave the Narrator's presence?
Believe it or not, we're going to suggest that the individual bits of transportation aren't really that important to the poem. Seriously. No joke. Rather, it's the abundance of imagery—when considered as a whole and in bulk—that truly matters.
The Narrator says, "I don't care how" while offering Marvin K. all of his options for leaving (37). From this, we can guess that it's the act of leaving that is most important, which is why there are so many ways offered to Mooney. The idea is to get beyond the how and focus on the actual act.
The reasons for this will vary from reading to reading, by which we mean reader to reader. If you see Marvin K. as Richard Nixon, then Seuss seems to be saying that Nixon needs to vacate 1600 Pennsylvania Ave. The way he goes—anything from impeachment to self-resignation to Ga-Zoom—doesn't matter just so long as Nixon gets. He chose helicopter if you're curious.
On the other hand, we can read Marvin as just a kid getting ready for bed (he is wearing purple pajamas, isn't he?). If we read the poem like this, then the modes of transportation suggest ways to make such a menial task much more enjoyable. No boy wants to go to bed, but we're betting plenty would want to take a Crunk-Car for a spin.
Both readings are perfectly acceptable. Feel free to see where your own reading takes you in regards to the transportation imagery.
Oh, and for your convenience, a list of all the ways Marvin K. may go:
Foot (10), Cow (12), Skates (17), Skis (19), Hat (21), Bike (27), Zike-Bike (29), Old Blue Shoe (33), Stilts (41), Fish (42), Crunk-Car (44), Lion's Tail (48), Mail (50), Zumble-Zay (58), Ballon (60), Broomstick (61), By Camel in a Bureau Drawer (64-66), Bumble-Boat (67), Jet (68), Ga-Zoom (72).