Porting PlayStation games as a means to entice PC gamers to buy new PlayStation hardware is a poor business strategy unless you incentivise them to invest almost wholesale into the PlayStation ecosystem (third party titles, subscription services, etc), effectively abandoning PC as their primary or preferred gaming platform. And that is not going to happen with exception to an extraordinarily small and likely measurably insignificant cohort.
While Sony's precise business strategy is impossible to know, the value of PC gamers buying PlayStation hardware is directly proportional to the net revenue generated from the hardware in of itself. At launch this is usually extremely low due to the manufacturing costs being at their highest, sometimes so high the hardware will be sold at a loss. Losses are recouped through software sales (first and third party) and long term strategy of building a sustainable ecosystem.
What we are likely seeing with these ports, and the fundamental reason to port at all, is the same reasoning Microsoft uses for bringing Xbox exclusives to the PC platform; the software revenue generated from an audience of new customers who did not and will not buy the hardware is significantly greater than the combined software and hardware revenue generated from customers who will and do buy the hardware for exclusives but refuse to invest in the ecosystem of regular software purchases and subscription services.
Or, to measure out your groups;
• Group A: Wants to play PlayStation exclusive software, but will never buy the hardware to do so as PC is their preferred platform.
• Group B: Wants to play PlayStation exclusive software, and will buy the hardware to do so, but will not play anything other than exclusives nor subscribe to services as PC is their preferred platform.
• Group C: Wants to play PlayStation exclusive software, and will buy the hardware to do so, in addition to using PlayStation as their preferred platform for all software, purchasing a lot of third party software for the hardware in addition to subscribing to services.
• Group C is your bread and butter. Group C is your sustainable business. They are your core customers. They bring in a large volume of sustainable money, primarily because they buy a lot of games for the hardware and subscribe to services. Sony get a cut of everything, including third party sales.
• Group A by and large is never, ever, forever going to become Group C no matter how hard Sony try. A very small cohort of Group C will, but a vast, overwhelming majority will not. PC is not a console, and the reasons people prefer the platform and ecosystem are not comparable to Xbox or PlayStation.
• Group B already exists, but their are a limited source of revenue. They buy the hardware, and they buy the software, but because of their set requirements they only buy 2 - 3 games per year (if that, as it depends on the appeal of exclusives). They are a poor source of sustainable revenue and will not become Group C.
Sony and Microsoft are thus challenged with the conundrum;
• Group B and Group C make up the current business model, bringing in X revenue per fiscal year. Group C makes up a vast majority of this revenue.
• Group B revenue is made up of Ya and Yb. Ya is software sales, Yb is a once off hardware sale. Ya is the most valuable of these two, by far.
• Group A has the potential to add Z revenue to the fiscal year through software sales, but currently brings in nothing as they have no access to software.
• In porting games Sony/Microsoft have the following situation; Group B will stop buying hardware (Yb), but will continue to buy software (Ya). They will also gain revenue from Group A, bringing in Z revenue from software sales.
• And so the question must be asked; is the potential revenue of Z greater or lesser than the loss of revenue generated by Yb (hardware), and how susceptible is Group C to becoming Group A.
The answer is assumed are;
• Potential Z revenue from Group A is significantly greater than the loss of revenue from Group B's Yb. Resulting in an increased total revenue from the two groups. In short: Z + Ya >>> Ya + Yb
• Little evidence exists to suggest that any significant cohort of Group C will transition to Group A, due the unappealing ecosystem of Group A's hardware. PCs largely do not offer the same service or device appeal as consoles. For Sony, their director competitor in this space is Microsoft, not PCs.
• For this exact same reason, Group B is extremely difficult to transition to Group C. They are not going to enter the same sustainable revenue stream. Group A most definitely will not.
If Microsoft continue this approach, it would suggest they have excellent internal data that suggests the above. It suggests that Group C will continue to buy Xbox, the exclusives, the third parties, the indies, and subscribe to GamePass and online and whatever else. And that the impact of also providing for Group A actually has negligible impact on revenue from Group C, and instead results in greater revenue as a whole.
I don't necessarily think Sony will follow the exact same model, but this is the most sensible reasoning for "why do they port to PC". More than trying to entice people to buy PlayStation 5 hardware they'll barely use.