It was totally low hanging fruit. Try building a search engine today. The barriers to entry are much harder. Finding useful sites and filtering out spam are much more difficult now than when Google started. The signal to noise ratio on the internet has plummeted.
This is what everyone thought in 1999. Search engines were a solved problem in a crowded market where there could be little room for new contender And whatever limitations we had in search were just inherent in how it all worked and we just had to deal with it.