The point is they got shit on a stick for him.Long story short. Young Tyler was not a fit for the Boston system.
"The second reasoning was whether Tyler Seguin’s work ethic and his style of play fit with the Boston Bruins. He is definitely a skill and finesse player first and was purely that as a young player in Boston. The front office may have wondered if his playstyle would fit on what was a grit grinder roster at the time."
Boston Bruins: Revisiting the Tyler Seguin trade with the Dallas Stars (causewaycrowd.com)