The 49's are in win now mode. They failed last season because they were down to their 3rd string QB, who also got hurt.
They are not in a position to mess around developing a QB for the future when they already feel they have that guy on the roster, as well as the depth that helps them as contenders in the now. Prioritizing depth over a developmental QB makes a lot of sense for them in their current state.
Lance has barely sniffed the NFL. He may not be the guy the 49's thought he was when they drafted him, but that doesn't mean he has no future.