You've pretty pretty much articulated one of the reasons for existence of ad tech industry. Inventory on the web is highly fragmented and ad sales one small sit

You've pretty pretty much articulated one of the reasons for existence of ad tech industry. Inventory on the web is highly fragmented and ad sales one small site at a time is not really scalable for anyone to make a living out of. Hence ad networks emerged to aggregate inventory. Now you probably have a "real" day job and don't really need to make even the website pay out, let alone make a living out of it. Not so for many other people who do make a living out of content.