Problem with those expensive treatments is that there are not that many cases. So profit from each is big but overall they add up to less. Getting everyone who can afford it on planet on some relatively cheap drug would be lot more profitable overall.
Get million out of thousand people or ten out of billion people... Later would be preferable.
Well there's also the third option of get a million out of a billion people. And that's only one side of the perverse equation. The other is rent-seeking. A treatment that needs to be redone or repeatedly boosted is far more profitable than a treatment that simply solves something once and for all, especially if that 'solving' treatment can be done cheaply.