There are thousands of directories, but not thousands of search engines. Other than the three search engines that I listed, you can't show me 100 other search engines that combined can drive 10% of the targeted traffic that the 800-pound gorilla can.
And there you go again. Not paying attention to what I write. I don't put all of my eggs in one basket. I just happen to be getting hundreds of thousands of unique visitors every month from the search engines that I do focus on. The only people I have ever met who claim to never focus on Google are the ones who do not know how to get results. Go ahead and focus on your thousands of directories. That and 10 cents won't buy you a cup of coffee.
The chances that Google will go out of business appear to be about that same as seeing you substantiate any of your wild claims, so focusing on Google is a pretty safe bet.