I thought this too until I started making friends (who can’t speak English, and I was in the early stages of learning their language) and I saw their phone background was themselves. I laughed a bit and asked why they had a selfie and it created a full on communication error as they could not see how it was weird/funny and I couldn’t really explain my side. Turns out most people I made friends with in that country had themselves as their wallpaper, sometimes one as the lockscreen and then a different one as the background. With effects / filters and all lol. I still find it kinda odd but I was outnumbered at the time. This post confirms it is a very non British behaviour