YouTube is the biggest search engine on the web. It controls over 40% of Internet searches, and with that it controls pay per call advertising (pay per call). PPC involves the advertiser paying a rate for every call through (CTC) in which the advertisers set. As their budget increases, their position increases, and as their position increases, they get more inbound calls.
One reason for this is scalability. Those who originally choose to advertise in search results and who were getting a ROI (return on investment) will decide at one point that they need to identify other advertising opportunities. With thousands of websites which have the capacity to display their adverts the advertisers can gain further exposure very quickly.
Another reason why advertisers choose to advertise in Google distributors websites is that it gains them further exposure. 60% of internet users do not use Google, so the advertiser can appeal to a wider audience through choosing to opt for distribution channels. Many website users may be looking to buy a product such as a phone, yet instead of coming across a website which sells such a product, they come across an article. If the article is on a website which contains Ad-sense then inevitably advertisers can use this channel to penetrate their audience.