Google succeeded because Yahoo used it as its default search engine for years alongside their directory. Google got enormous exposure from that at a point when they needed it. Imagine if your little startup had a "How about you try us out ?" on google.com, permanently. Plus, eventually, Google got better at Search.
At the same time google was stocking every level of their org chart with legendary engineers, Yahoo appointed a demented Scientologist from Hollywood as their CEO. Yahoo for some reason thought they were in the show business. They could not have succeeded on that premise and it’s a miracle the company even survive the reign of Terry Semel.