I mean open in a more general sense, not of its source code. If the platform invited the user to set a default, or was "biased towards their user's preferences

I mean open in a more general sense, not of its source code. If the platform invited the user to set a default, or was "biased towards their user's preferences", as most would select google, google would be the "natural default". There is a sort of mild rent-seeking / racketeering in asking google to pay to configure a service Apple provides, to a default Apple's users would chose for themselves.