First, it's about the historical era. Demon Slayer takes place in the Taisho era (1912–1926). During this time, Western-style suits and fedoras/panama hats were the peak fashion for wealthy Japanese men. Muzan is just dressing like a rich guy from his own era.
Second, if you look closely at the details, their outfits are totally different. In Smooth Criminal, MJ wears a solid white suit with a blue shirt and a signature armband. Muzan, on the other hand, wears a black patterned blazer with white pants and a black shirt. The only similarity is that they both wear a hat.
They actually just shared the same vibe inspiration: Gangsters. MJ’s look was inspired by 1930s American mobsters, and Gotouge (the author) gave Muzan a sharp suit to give him that intimidating, 'Mafia Boss' or Yakuza-like presence. It’s a common trope for villain leaders
