Is a music magazine or a radio station a gatekeeper because they can only showcase a limited number of artists, or are they a curator because they help the end user sort through thousands of bands to find the ones they would like to know about?
Even record labels have a role to play in the curation game. Smaller independent labels like 4AD, Wax Trax, Factory, SST, and Alternative Tentacles became valuable to fans in the '80s and '90s because their labels each created a "sound" of their own. You could confidently buy a record from a band you'd never heard of and know that if you liked the other bands on that label, you'd probably like this new one.
Curators provide significant value, and earn their keep. It's only when the curator turns into a gatekeeper and becomes a hindrance instead of a help that the problem arises.