I think advertisers haven't adapted well to the youtube market at all. They're still operating under the TV model where ad breaks are an expected part of the tv viewing experience and don't understand that on youtube they are intrusive as hell . This also couples negatively with advertisers viewing youtube apparently not putting any limits on ad length as an opportunity to deliver a sermon. I think most people would be annoyed but not totally put off by a couple 15 seconds ads but the issue is that users just have no idea if they'll get a 15 second ad or a 15 minute ad so they skip everything out of extreme frustration with the entire experience.