DISCLAIMER: I am biased towards the Kaan. With that out of the way.
Two points come to mind:
1. PAF is obviously hedging their bets. They want to keep their options open.
2. Kaan is not going to be ready for the PAF before the late 2030s/early 2040s (I'm assuming including the engines), so if PAF wants a FGFA before that, they'll need to get the J31.
The Turks have a habit of constantly compressing timelines (by years sometimes) so late 2030s may become early 2030s. In which case, PAF might drop the J31 altogether if they find the Kaan to be of sufficient maturity.
It is my opinion that if both the J31 and Kaan were available at the same time, the PAF would go for the Kaan in a heartbeat since it meets the Azm-like ASR more closely than the J31, and has "western-adjacent" technology. Roughly speaking, Kaan is Turkey's J20 so they are putting everything into it. If their plans come to fruition (high likelihood because of all of the access that the Turks have), the Kaan is going to be a beast.
Keep in mind buying the Kaan means buying its range of Goktug missiles too, which are Turkish AIM9X, AIM120D, and a to-be-seen very-long-range missile.
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I feel like the PAF would like to have a "western" set of missiles after the F-16 based AIM120s expire.