Probably google's profit is much bigger in search market because you are more directed to searching for information on a service you may buy (and so, a company may be interested in advertising) than when you are watching a youtube video.

From my personal user point of view, i have searched very few times in youtube (just as an example) for a company or a product and then clicked on an ad. Just on the other side, i have done such thing many times on google.