1. They were the simplest to use at the time. All the other search engine things had a lot of frills and pages and ads and so on. Google was just very plain, and as a result, simple
2. By default, they included ALL the words you typed in. Competitors at the time were trying to maximise search results by searching for each word individually, which led to a lot of irrelevant results. Just by including all the words in the query, google had a much better hit rate
All the rest was unimportant. Those two simply front-end decisions made the google search engine loved by the geeky anti-corporate people who ruled the web at the time (slashdot, linux advocates), and they recommended it to everyone who was joining the net. By appealing to the geeks, who then acted as the authority figures to the normals, google was able to take over the search market back then.
It was really not that complicated.