Apples and oranges. You are making an invalid comparison.
One centers around the right of association while the other is clearly 1st amendment protected political speech.
Nope, the 1st Amendment only applies to the federal government, specifically congress. (Before that evil called incorporation
, anyway.) Even if the first were incorporated against the states it still does not apply to private persons. The issue here is really that of rental agreements, if there's no prohibition in the agreement WRT political signage (or, perhaps, a sort of upkeep clause) then the owner doesn't have a leg to stand on; whereas the issue in the baker's case was the ability of a business to refuse service to anybody.