It's absolutely not as simple as that lol, I'm sorry but this black-and-white logic is just laughable. Just because they're currently opting for AL-31Fs DOES NOT mean that performance-wise the WS-10 is worse.B/c evidently crappy 30-year old engine is still better enough for the specific application, despite not being domestic.
Which is risk, but also money going elsewhere and political backlash.
Given that Al-31 is old and is clearly weak for this aircraft, it should give you an idea or two on how "suitable" WS-10 is for the job to this very day.
It could be due to a variety of other reasons, costs, logistics, other political pressures, etc. They are way more likely as actual reasons and I can't stress enough how ridiculous your thoughts train is.
