Conan O'Brien got the Chuck Norris fad started with a sketch he'd do where he'd interrupt boring interviews with a lever that would play clips of Walker Texas Ranger.
After that the internet ran away with it, but yeah it's a meme as old as time
Yes, something awful writers are not surprisingly late night fans. They saw what Conan was doing with Walker, and they ran with it. Chuck Norris was already a forgotten nobody in 2005, it's not like he just popped back into the lexicon out of nowhere. Conan reminded people of Chuck's cheesy badass schtick, and after that the jokes rolled in. Vin diesel jokes were getting old so they replaced him with Chuck