None of the choices of content blockers in Safari successfully block the majority of ads on the internet.
Furthermore, it's not just about the surfaced ads. Even if you use uBlockOrigin, search engines like Google optimize for ad clicking, which will affect the search result ranking even if you have ads blocked. As a result, search quality has been steadily decreasing over the past decade (there have been hundreds of highly ranked HN discussions on this in the past).
Finally, uBlockOrigin is an amazing tool developed by 1 person. There is always the chance that, in the future, there are developments in browsers or ad-serving technologies that render it obsolete (e.g if Google decides to make a breaking change to the Chrome Extension API, like Safari did). In that case, it would be worthwhile to have alternatives.