So, why does each second have a photo/link instead of most of them being empty other than for 925 of them?

Good luck with the get $373,680 [1] richer scheme..

Edit: aha, uploading and overwriting someone's content is free, to have an overwrite-lock one has to pay for it... Well I guess you were expecting a gold rush, but with so little uptake people seem to be thinking "why worry, chances are my link won't get overridden, and if it does happen I can just overwrite someone else's."

[1] (864+1) x 864 / 2