In Maniac Magee by Jerry Spineli, why did Maniac choose The Little Engine That Could as Grayson's first book?

Jerry Spinelli never writes why Maniac Magee chooses The Little Engine That Could.  Maniac never explains it either, so it is left up to the reader to hypothesize a reason.  

I think Maniac chose the book for a few reasons.  First, it is not a difficult read.  That is important though, because Grayson is learning to read for the first time in his life. Maniac needs a book that is accessible for a beginning reader. 

Second, the book has a motivating message.  The engine keeps up positive thoughts and is eventually able to accomplish a large goal. That is the message that Maniac wants Grayson to learn.  Reading may seem like a daunting task, but if Grayson continues to think that he can do it, then he will be able to really do it.