Indeed there’s no technical reason for it to not be displayed, but then one has to take into account possibility of tags obstructing parts of cover image as I’ve noticed here:
I don’t know if I’m misremembering stuff, but I think there was a time where some tags appeared on right hand side of the cover image. If that’s still the case then designing cover image with all the possible combinations will be a bit harder (or users will have to edit and adjust based on what shows up).