[0] International First, not what is called First in the US.
It's not just about time or inconvenience. Nationals of Ghana can transit the UK airside (at the same airport) without needing a UK visa in most cases, but changing airports means they are more likely to need a UK visa (there are fewer exemptions).
I also challenge the idea that Heathrow is ever cheaper to get to than Gatwick. The Thames Link service to Gatwick is far cheaper than the Heathrow express, much faster and more pleasant than the Piccadilly line, only the Lizzie line makes Heathrow as cheap and easy to get to by train as Gatwick.
It’s too bad Norwegian shuttered their long haul service between Gatwick and NYC/BOS. It was affordable, comfortable and convenient, so of course it went bankrupt. Now the best options are out of Heathrow (my favorite is now British Air, as long as AA isn’t operating the flight…).