few reasons:
1. what flintoid mentioned
2. russian vs yugo (yugoslavia has been known for not being able to produce high quality alloy steel. lack of natural deposits of molybdenum, chromium, wolfram) therefore "Heavy Duty' 1.6mm receiver is extra heft to compensate for lack of strength. do you like extra heft/weight?
3. true russian Izhmash Built rifle based of AK100-series of guns, which are more modern revision (shortcomings o AK47s/AKMs/AK74s corrected and improved upon) vs whatever unknown revision these PAP AKs are using.
I don't believe either will have that much of collectible value since neither are even remotely rare and market is flooded with these rifles.
also level of interchangeability. as i mentioned there are millions of Saigas circulating and majority of parts for those are very much interchangeable regardless of the caliber - easier to find down the line.
amount of after-market parts for Saiga is somewhat higher too i would think