>>3383455Back when the game first released, their playstyles synergized with each other quite well, so you were very likely to see them next to each other in any given session. As per the first rule of shipping, if any two characters spend more than a few seconds in each other's proximity in any context, they must be in love, so the fans ran with it. I haven't actually played the game outside of Junkenstein's Revenge and Uprising for a very long time, though, so I don't know if this dynamic is still viable. But even if not, it's effectively been locked in out of habit by now.
Canonically, it actually gets kinda weird, because we only know of one instance in which they've officially met, and Pharah was a preteen at the time.