Why? You might as well say that a good product development team would never go for TV adverts and would just rely on word-of-mouth.
For any search query, there’s only one #1 spot in Google. Only one website can be there. You might be in a very competitive sector where there are dozens of good websites that you’re up against. You can have a fantastic website, a great product and hundreds of links but still not make it into the top 3.
If advertising brings in more money than it costs you then it’s a successful strategy.