I use stackoverflow often. As a web developer, I notice nowadays many sites use bootstrap to be responsive web site. When you reduce the size of browser, you will see a little bit different layout and it fits to browser. Especially it's useful if you are in tablet or smartphone. I saw https://meta.stackexchange.com/ changes it's header content when you reduce browser size, but not full content. Footer exceeds from browser screen. Is there any reason why stackexchange.com sites are not responsive/mobile friendly?
PS: I'm not complaining. All stackexchange sites are cool. Just want to know reason. Maybe they are planning to do it.
EDIT
I don't use mobile version of stackexchange sites. So I didn't know that there were different mobile version (and app) of the site for mobile devices. My question is only for desktop version. It's not fully responsive. I mean There shouldn't be scrollbar horizontally (Bottom of the screen). Of there could be scrollbar within question/answer body.

