The problem is they are horrible at trading, both when they trade away players and when they trade for players.
Trading a 4th round pick for Lance at the time was questionable but reasonable despite the fact he was probably worth more of a 5th or 6th (again, before we saw him play and realized he wasn't).
Trading a 4th round pick for Mingo was stupid, especially with the way last season was going at the time. That is not a knock on Mingo but more about just not being worthy of a fourth round pick.
They traded Cooper away a few years ago for a 5th round pick and Cooper was (and may still be) a much better receiver than Mingo.
If they trade Parsons, I won't be surprised if they don't even get a 1st round pick despite the fact he should be worth at least two 1st round picks and probably more.
The front office failures with delaying contracts that they know they are going to ultimately sign which leads to them paying a lot more later, overpaying in draft picks for players they trade for and getting underpaid in draft picks for players they trade away are well known.