Can there exist such a search engine that can stay objective in the long haul?

I'm not particularly mad about Google putting ads, since the world is waking up and I believe in the future it will be obsolete.

But as I see it, the problem is that all search engines have this issue where the more volume it has, the more lucrative it is to game it. Let's say DuckDuckGo becomes vastly superior and widely used, what's preventing it from becoming another spam machine where SEO is the name of the game.

As I see it, there's no really good solution here. Maybe some open source indexing algorithm and a different search engine for different types of content.