What's the point of having Fuck You Money if you can't say "Fuck You?" Your value assessment isn't taking into account the value of destroying old Twitter, of removing a major bullhorn in the information environment away from people that Musk probably considers adversaries at best, and malevolent actors at worst. Simply standing up his own competing platform would not have accomplished this.
“Elon made an obvious mistake? Oh no, newb. Look on this other indicator that reinforces my bias.”
Though Elon Musk's purchase of the company was entirely in his own self-interest, and unfortunately, it's serving him well so far. Buying a company for a fraction of his personal wealth and leveraging that into having the president as his personal servant is one of the greatest investments in American history.