As a longtime Smallville fan, I will defend a lot of things about that show, but I will never forgive the CGI Superman, who ironically enough, was Brandon Routh, since they re-used both the suit and his CGI model.
I love Tom Welling, and visually he made a great Clark, and could've been a great looking Superman, but anyone who knew anything about him knew he was not going to wear the costume at all. After season 7, the new producers changed a ton of things that didn't make sense, and did a bunch of things that didn't make sense, but I truly believe that had they had their way, and had Tom not been so opposed to the idea of dressing up, that we would have seen more than just a Jacket or Trenchcoat costume.
But then again, there was the tricky situation of them not being able to say the name Superman because of legal battles, so I imagine that had some role to play as well.