Can anyone explain DiPietro & Luongo to me?

i watched a little video documentary about Rick DiPietro which got me wondering what exactly the ‘rationale’ was for dropping a highly promising luongo for dipietro was? i know that era is different from today, but im curious if any older isles fans can explain this seemingly bizzare move to me. i’m wondering if there was any internal organization politics that played a role in this weird decision. thanks :)