For big, long-established brands, advertorials aren’t necessary because people already know and trust the brand. They’ve already established a presence in their industry and they’ve got a sizeable following.
For the rest of us, advertorials help establish that coveted industry authority.
We should clearly define what we’re talking about here, first. We all know what advertisements are. They are commercials that tout your brand, how great it is, what deals you have going on, how you’re better than your competition, etc.
Advertorial videos don’t do that. What they do is report on some aspect of your business or demonstrate your expertise in your field, instilling trust in the people watching it. Their main focus isn’t on trumpeting your brand, but on teaching viewers something they didn’t previously know. Therefore, watching the videos are beneficial to the viewer. If viewers learn something from your advertorial, they are left with the feeling that they’ve actually gained something of value rather than having the feeling that they’ve lost time watching a commercial.
They are made to look like a journalism broadcast, so you have a "reporter" interviewing people and saying things about your brand in that newsy way reporters have. When people see this style of journalistic type reporting, it gives them the sense that what they're seeing is factual.