Sometimes it’s just about using the path of least resistance. I’ve also contributed to Apple Maps’ and Google Maps’ data, even though I’d prefer to exclusively contribute to OSM and other open platforms instead. But, it was just easier to go through a quick form in the (Apple|Google) Maps app, because that’s where I was at that point in time. Maybe the excuse is laziness and/or force of habit?

Edit: I also imagine the reach of the mainstream platforms to be much higher (e.g. Windows vs. Linux or Google Maps user reviews vs. <is there even an alternative?>).