It’s my understanding that the executive does not have the authority to unilaterally change official geographic names. As of my writing this, the name “change” has NOT been adopted by the United States government. Congress granted that authority to the US Board of Geographic Names in 1890. Unless accepted by the US BoGN, it changes nothing. I suppose Congress could rename it if they passed a bill that the president signed into law overriding that authority for that specific case, but until they did so, it’s not official.
Here is the link to the US Geographic Names Information system page showing the current official name of the Gulf of Mexico: https://edits.nationalmap.gov/apps/gaz-domestic/public/search/names/558730. Note the list of accepted variant names, which still doesn’t include “Gulf of America”.
Google are saying here that they will only change it on maps if it’s made official by the US Government, which has not happened yet. That’s why they haven’t made any change yet, and won’t unless Trump gets the US BoGN to do his bidding.
That’s my read on it too. Trying to have it both ways, and not exactly succeeding at it.