The only thing Google had going for it was no ads and a committment to not be evil.
That's all it took to topple the leaders.
No, those are not the only reasons. There is a more important one: in its early days, search results from Google were noticeably better than those from other search engines. Google’s PageRank algorithm was ground breaking. It allowed the search engine to rank webpages fully automatically without human moderation and without using some obscure heuristics with unstable performances.