There are many different types of traffic, as there are different earning models.
Few portals do any type of branding, but if you have a site with quality information that changes frequently its a viable option.
In branding the initial traffic usually doesn’t convert too well, as you are driving numbers. If you do it right, as the business matures, the traffic will become better and better in quality.
Branding takes time and money and time and more time, and then more time. Much of that time there won’t be much profit because you plow money back into the business, keeping the portal fresh and growing it and the traffic.
My guess is that the portals listed with lots of traffic are either well branded or just have junk bulk traffic. Generally buying such high amounts of quality traffic is not very feasible, although it is possible.
Junk bulk is never good, not for branding either.
In past years people used to laugh at me because I applied branding to a portal. Nobody has been laughing in some time.
It is one explanation for the high visitor numbers. But as pointed out above, you don’t need that many visitors to be profitable. Targeting your site well will do the same with a lot less visitors.
Others do well with linking schemes, but you need to be watchful doing that nowadays, google is very leery of links anmore. Doesn’t mean it can’t be done though, just stick with quality.
There are many ways to do create a profitable business, and everyone needs to figure out what suits them best.