I get your point indeed, and we take users' privacy very very seriously. I think the main problem here is that Pixelfed doesn't support the semantic to allow users to opt out from search indexing. In the case of mastodon, we support this feature.
The same set of settings that blocks google from indexing you would also block fedisearch from doing so as well. We have a insignificant amount of traffic compared to google... so if being indexed is the main worry, we feel we shouldn't be the main antagonist 😅