It's because so far, I have been able to avoid storing user uploaded images. Everything in relay tools is image links. The reasoning for that is to avoid cloud lock-in and image synchronization or processing within the cluster. (each frontend would need a copy of these user uploaded images once you go down this path).
favicons kindof breaks this, ... more likely i would just pick a better icon than the 21. like a checkmark, because self hosting is king, and anything making that more complicated is not ideal.