They're running a marketplace to sell stuff...

Yes a store front charged a premium to host something on their platform. Like you can levy that complaint against practically every e-comerce website on the internet from e-bay, etsy, amazon, steam, overstock, etc.

And they do link to the creators websites. You can click through to their vendor page which can have a link to their personal website. https://filtergrade.com/vendor/carlos-viloria/