I don't know if you're familiar with the company AllAdvantage but in 1999 they tried to pay people by the hour to have a banner ad displayed on their computer, up to some number of hours per week.
One of their problems was that paying ad viewers directly incentivizes fraud. There were many apps to make it 'look' like you were engaged, while you actually weren't.
Similarly, in Bill Gates' book "The Road Ahead", he proposed the idea of emails that come with money attached to them. (i.e. You are paid to open and read advertisement e-mails.) I don't know if this was realistically tried anywhere.
Fraud aside, I think it's hard to avoid falling into one of two boxes in paying people to watch ads:
1. They pay so little that it's not really worth anyone's time.
2. They pay enough to be interesting, but it means people will view ads for products just for the money and the effectiveness of the ads will be very low.
I think the industry has found that the ad "tax" (i.e. ads in the middle of content) is the model that actually works. And in this model the bulk of the ads' cost is paid to the content creator who is in theory providing a good enough audience for that particular advertiser, which is the actual value to the advertiser.