Go and read this GRRM interview with the NY Times:

When I returned to prose, which had been my first love, in the 90s, I said I’m going to do something that is just as big as I want to do. I can have all the special effects I want. I can have a cast of characters that numbers in the hundreds. I can have giant battle scenes. Everything you can’t do in television and film, of course you can do in prose because you’re everything there. You’re the director, you’re the special effects coordinator, you’re the costume department, and you don’t have to worry about a budget.