Maybe they try that in practice and he isn't good at it. I love Tanner but he never came across to me as someone who was a great decision maker on the fly.
I am not a big fan of Sanford as a playcaller...but part of this is I don't think we have the personnel to run the offense they want to run. It is easy to take chances when you have a couple WRs who you trust. I like CAB but he is not there yet and he isn't on the field enough to force defenses to honor him in the gameplan. Morgan is very good at slants and high percentage throws but if all you have is running plays and no deep threat they can keep guys close and basically clog up the lanes.
Now a good OC would try something else to maybe throw a wrench into what the defense is doing (Purdue was begging to be screened on as was Bowling Green) which is where my issue with Sanford is. (and sometimes Fleck) You have to be able to say "ok our plan isn't working, lets try something else". Now again, maybe they don't trust that Morgan can make those changes (they obviously have never been big on letting Morgan change plays on the line and even they have rarely done it other than to change the formation) but then that is a whole different set of problems. As the OC though you really aren't putting him or the team in a position to succeed...
RememberMurray is right though in that everyone always whines about the OCs. Every OC (and DC outside of 1 for that matter) we have had has been attacked for lack of creativity and vanilla offense. I know people whined about KC (I haven't seen one OC not whined about since Glen Mason was coach) when he was OC and if everyone got their wish tomorrow and Sanford was replaced by Simon it would take at most half a season for them to turn on him too. Fans always think the grass is greener...the backup QB is the answer, a different coach is the key and different coordinators are all that is holding us back from championships. When we run high flying offenses and lose the fans say "why can't we just be like Iowa and run a boring offense and win...winning is all that matters!" and then when we do that it is "ugh this is so boring!! The coaches have no creativity so our wins don't mean as much!!". Fans are just a reactionary bunch.
Now just because the team won doesn't mean the issues don't exist, it just means you are willing to put up with it because the win is what matters. If the team doesn't win though that is when it becomes a problem. Personally I hope he is not the OC next year but unless something really bad happens in the Big Ten season I don't want him fired until the offseason.