Presumably a Governor has a wider view than an agricultural commissioner. For example, one would not expect an agricultural commissioner to focus on drug or gun law enforcement.
They are both elected positions with separate offices, so the Texas Ag Commissioner is not a subordinate of the Texas Governor, for example. The Lieutenant Governor in Texas has quite a bit more power than the Governor in fact as their office sets the agenda for the Texas legislature which meets only once every two years though for several months. The Texas Lieutenant Governor is also individually elected.