> In my view, its a bit weird.
I think it's a matter of opportunity cost. By giving away an art-finder like this for free, using the pictures of the sculptures, you take away the incentive for commercial provider to do the same thing.
Commercial providers would have to pay money for the pictures and thus, a free app is costing the copyright owner (or the manager of the copyrights) money indirectly.
And even failing that: By publishing this on the internet, even if you are offering it for free and without ads, you still create value for third-parties with this content (carriers, platform owners, whoever is injecting ads into your content, etc), so as monetary value is created with this content, the management agency wants to be paid and if they can't be, then they want the content off the net, so other content might appear where they are getting paid.
At least that's what I believe to be the reasoning.