I mean, it's a two way street. Maybe Baun just saw a better opportunity with Philly since he is a much better fit for there scheme and is likely to get many more snaps?
Willie Gay, Jr. is a pretty big upgrade over Baun as a LB. And Young may be lazy, but he's likely going to get you 7 to 8 sacks even as lazy as he is, and he fits our 4-2-5/4-3 scheme where as Baun was going to get very limited snaps on pass rush only downs. Baun is a better special teamer, but he was likely at best going to get 7-8 sacks too and for the money you add Gay who is a much better LB and can likely play special teams too.
I would have like to keep Baun as a situational pass rusher and special teamer, but I can see the logic behind replacing him with Gay and maybe Young. And it may be that he just had no desire to stay here given that he is not a scheme fit in New Orleans.
As much as you let go a guy that may be an up and comer, you replaced him with a guy who clearly is an up and coming LB. And, Gay may even have some untapped pass rush potential.