Bases on [my research](https://www.quora.com/Why-does-the-logo-for-7-ELEVEn-end-with-a-lowercase-n), this was largely a graphical design decision.  It may even have been the wife of the company's president that made the suggestion, but either way, designing logos is an art of both functionality and appeal.

Consider brands that spell their name wrong like Froot Loops, or use bright colors to catch your eye, I guess that's Froot Loops again.  Companies will do anything to keep you looking for even just one second longer, and that starts with logo design.

The most interesting possibility, from the same link, is that the word *ELEVE* in spanish means Elevate, although it would be more interesting as ELEVETE, elevate yourself.  Of course in french, élève means student.  

Keep learning!

I once hear that it was the wife of the company President in the 60's that thought that making all the ELEVEN capital letter will not be cool.and provide good aesthetic value. So it was suggested that the N should be made in lower case to make the logo more beautiful to the eye