The ability to do responsive design is fairly recent and, in many aspects, unavailable in any version of Internet Explorer which is always years behind every other browser. Many properties to implement it work well in any other browser but were unavailable in IE until IE10 or, sometimes, IE9. So writing code that works in modern browsers will still require extra effort and writing to make that same code work in IE, just as in the past.
There is also more effort involved in creating a responsive site. While having a mobile version is helpful, serving it integrated into the whole site is still quite different. It's not a matter of flipping a switch to do so and is almost as bad as having to write multiple versions of the same site.
Large sites, like you mention, have a lot going on and integrate content from many different sources. Trying to make all that responsive could be quite an ordeal, especially considering that their base code is probably several years old. Just finding someone who knows how to do responsive layouts well may be difficult. We're all still learning.