pull down to refresh

From a UX and ideal standpoint, yes, I agree, but it isn't that simple because of scaling challenges.
We need servers/hosts in order to scale anything many people want to use together, and the service of hosting is regulated in most countries.
Additionally, most hosts don't want to have to host some kinds of data, which means it could/should never make it to the client at all.
Automation on the client-side could also be a challenge, and you def dont want manual moderation for some images...