E.g. Being able to "blacklist" certain domains from results.

Same thing applies to youtube. You can not permanently block/remove/disable channels from being present in the content results/feed.

I think that deep-down Google high-ups "know" that giving some of these "basic" usability features would essentially disable their control of the content that they push to you. E.g. imagine publicly-shared black-lists of bad domains and bad channels that one could subscribe to. Similar to the ad blockings lists that have generated a bit of a thriving ecosystem. I.e. smart people would eventually use this basic "building block" to build content-control that would be more decentralized/democratic and really personal.