Google realised that the key use case for search engines was discovering websites and the information on them.
So they simply made it easier to do this by focusing on the search bar - and nothing else.
This might sound obvious, but Yahoo at the time had buttons and links everywhere - as well as their own search bar.
Yahoo was too cluttered. Users had a degree of decision overload, which created friction and meant it couldn’t be used in the same subconscious way that Google can be.
Today many of us have a deeply ingrained habit of reaching for Google as soon as we have a question. You may not even realise it. This kind of habit is incredibly difficult for competition to break.
So Google won.