Oak trees are more closely related to palm trees than they are to pine trees. It would be pretty arbitrary to exclude monocots but still include magnolids and gymnosperms.

Even from a purely structural perspective, they’re all tall and have wood and leaves. Palm trees and banana trees don’t have woody branches, but joshua trees do. I guess there’s a difference that no monocot tree has heartwood, but you’ll still need a chainsaw to saw through the trunk of a palm tree.