There is only one legitimate answer to the WHY...
Obama got the secret service he wanted!
The only thing the secret service did wrong, like a few others in his admin, is putting their incompetence on display, so they will be replaced by other incompetents, with one admonition “don’t get caught”!
I choose to believe the SS just no longer gives a damn about the incompetent corrupt scoundrel that is the President.
Why bother?