The off-season is a time of hope. There are fans and media from every team, Lions and Saints alike, who are talking about the potential of their draft picks, the development of their young players, better luck with injuries, tweaks to improve their offense/defense, etc.
For this reason, the off-season hype is focused around the players with more upside. Per your own statement, Brohm and Edwards appear to have more upside.
Is it a reasonable idea that Fitzpatrick starts? Yes.
The problem is that a focus on Fitz being the starter will ruin the hype of maximizing on our potential. Officially, the QB competition is still open, and he's still sharing reps. There's no need to burst the optimism bubble when we haven't even made it to preseason.