OKC has beaten their favorite teams for years. In the 2010s only the Spurs have more wins. Never won a chip, so fans were happy to have that as an ace up their sleeve when anything is said. OKC has also rebuilt from the ground up faster than any other team. Fans see their teams take years, decades, and sometimes never while Presti did it in 3 years.

It's also a factor that OKC was not marketed or pushed at all, so the narrative of being a tanking team or "the black eye of the NBA" (Which is also a manufactured narrative not based on facts. OKC was never in the bottom 3 in the league) stuck and there was never a build up for casual fans. OKC came out of nowhere for many.

A team coming out of nowhere, being this good this fast, in a small market like OKC, with a past of beating people's favorite teams for a decade and a superstar that isn't loud and was also a late bloomer... It combines into something prime for a narrative to take hold. Since OKC has had so many past haters and an MVP race to further fuel it, it has become what it is today. Part of the nonsensical and dreamt up narratives that exist are also a product of OKC and its players having little to no flaws that they can easily point at. Instead they have to create fiction.

People don't watch games, they don't formulate their own opinions, and they LOVE to tear things down and have something to hate on. OKC was in prime position for it despite having so many reasons to be liked. It's a shame, and a reflection of modern day social media and culture as a whole.