Because the “industry” has passed him by. Marleau has had a stellar career, but it’s like watching an old timer who was at the top of his game in the 80s and 90s struggle to work Excel or a Word document, yet he keeps getting the lead on these big projects despite there being younger, more capable employees out there. Marleau, like the business man may still be able to offer sage advice and tutelage, but he should not be the one doing the actual job.
As for the rest, aside from it being dismissive of any new blood or ideas, I’d argue that the new blood DID figure it out, but the dinosaur at the helm self-sabotaged.
Leafs have gone back to “old retreads” like you want (Fletcher, Burke, Wilson, Carlyle) and all of them failed to even make the playoffs in a full 82 game season. It took new blood Shanahan coming in and putting this team through a much needed rebuild that has us where we are today.