I really don't think that's the chief reason. A very tiny number of Facebook users save images locally as it is, and by switching to webp Facebook really does s

I really don't think that's the chief reason. A very tiny number of Facebook users save images locally as it is, and by switching to webp Facebook really does save them a tremendous amount of money. Also, since webp is an open format, it's not like users can't use very easy converters/viewers to make webp quite usable. I don't feel like this move is significantly more than an economic one.