But if you never use a character, how are you going to know if they're popular? Black Widow got the extra exposure of the MCU and her popularity has hit a high. The same with Hawkeye. They were fairly popular but the potential probably wouldn't have been realized if they hadn't been given some kind of chance with the new solos. Red She-Hulk's solo outsold Captain Marvel (according to an interview with Kelly Sue DeConnick on CBR) so why isn't she appearing anywhere when logic says she's bankable?
Anonymous

brevoortformspring:

This is such a crazy question to me. Clearly we have a very good idea as to how popular characters such as Red She-Hulk are, based on the sales of their most recent titles.

We publish a lot of projects featuring a wide assortment of characters. And not all of them stick.

Also, and I think this is pretty obvious, the sudden spike in interest in the Black Widow and Hawkeye has little to do with comics (though their well-crafted series take advantage of this) and everything to do with film.

It’s largely beside the point, but I want to clarify my comment, because it was taken out of context.  

This was at a panel about broadening comics readership – efforts to make our industry and our products more welcoming to those beyond what is often called the “core demographic." 

I offered that I felt Marvel was seeing and responding to the calls for diversity and that things like engaged and active fan bases and digital sales seemed to be part of the decision making metrics.  When I brought up Red She-Hulk, I explained that both books had been hovering around what has traditionally been considered by the pundits to be the cancellation tipping point.  RSH even outsold CM one month, by a slim margin, according to the ICv2 numbers, but CM was getting a new number 1. 

My point was that there are clearly factors in these decisions beyond cold (and often, I’m told, inaccurate) sales charts, NOT anything about the relative merits of the individual characters.