As it says in the Serpent statement, he wants to explore different business interests.
Ralph is a grown man with a family and maybe it's time for him to do something that will allow him to provide for his family after the racing days are over.
Maybe he's going back to school? Maybe he starts a company?
Maybe he got offered a job that goes beyond driving, like R&D, marketing , etc.?
I don't think he just quit Serpent to go somewhere else and do the same thing again.
Just my 2 cents.