why are the leafs giving up all of that just to get worse?

Keith isn't waiving to Toronto. He wanted to get closer to his family and this isn't what he wanted

Why not? At least it's not a first overall pick... lol

well, the getting worse part is why not.

Oilers dont do that Toronto deal. Thats a garbage trade. And a massive overpay by Edmonton

Leafs do not do that trade
1 - Keith is not worth the money
2 - Keith wants to be on the west coast (family)
3 - Leafs are not giving up those d-man
4 - Leafs don't need Yamamoto, they already have players of this nature on the team and in the minors do not need another

leafs flat out decline

That's a rare bad deal for both oilers and leafs. It's tough to do that but you somehow managed to.
Oilers don't need any more young dmen, leafs need to keep theirs.
Leafs don't need any more young forwards, Oilers need to keep theirs.

Awful trade for EDM. EDM pays premium assets for leafs scraps