They’re called Hoosiers not Indianans.
Politicians in particular like the theory of hard-working Indianans. Governor Evan Bayh used it on a quiz show ("Bayh Shows he's a Hoosier Quiz 'Kid'") where he explains the term "hoosier" as deriving from the canal builder, Samuel Hoosier, who "favored workers in Indiana and they became known as Hoosiers." With politics and state pride in his heart, Bayh continued, "We'd like to think it's synonymous with good workers."
In sum, "Hoosier" is a nickname and "Indianan" would be the proper terminology.