It's totally plausible Reed Richards bought the Avengers Tower and it'll soon become the Fantastic Four's headquarters, aka the Baxter Building. Marvel previously announced a new "Fantastic Four" movie is in the works, with Jon Watts, who directed Marvel's "Spider-Man: Homecoming" movie trilogy, set to helm the film. Watts has since dropped out, but the movie is still in development. Since the Baxter Building is supposed to be located in Manhattan, just like Avengers Tower, it's easy to see how the two could be connected.
And that's not all! An easter egg in "Spider-Man: Far From Home" may point toward the Fantastic Four owning the Avengers Tower in the future. At the end of the movie, Spider-Man swings by the newly redesigned building, and, as first reported by "Fan Fare, in the background there's a sign that reads, "We Can't Wait To Show You What Comes Next." Underneath the sign are the numbers one, two, and three. There's also an arrow pointing toward a question mark. Fans think it's supposed to be a number four, which could be a Fantastic Four tease.
In "Doctor Strange in the Multiverse of Madness," Jon Krasinski cameoed as another universe's version of Mr. Fantastic, so the characters are definitely top of mind for Marvel.