Convenient as it was, Fong doesn’t think the inclusion of his config was the main factor in the rise of WASD, and I’d agree. By the time Quake 2 was out, WASD was starting to feel like common knowledge. I used it, and I don’t remember hearing Thresh’s name associated with it at the time, though it’s possible his configuration entered my consciousness two or three people removed.
And yet games, strangely, took a while to catch up. Carmack may have bundled Thresh’s config with Quake 2, but when it released in 1997 the default controls were still arrow keys. A year later, though, that changed. If Thresh's Quake tournament win was WASD's first watershed moment, the second came in 1998 with the release of Half-Life. The Quake and Doom players at Valve—perhaps influenced directly or indirectly by Carmack, Thresh, and other top Doom and Quake players—included WASD in Half-Life’s default keyboard and mouse config, which helped solidify it as the first-person shooter standard.
Valve engineer Yahn Bernier checked Half-Life's original config file for us and confirmed it included WASD. "I remember finalizing this file (maybe with Steve Bond) during the lead up to shipping HL1 but don’t recall specifics about when WASD was settled on or really why. We probably carried it forward from Quake1…" he wrote in an email.
The same year, and less than a month after Half-Life, Starsiege Tribes also made WASD default. Quake 3 followed suit in 1999, and WASD's popularity grew even more. It was also the default binding in 2000's Daikatana, but Half-Life, Tribes, and Quake 3 probably had a bit more to do with its popularity.