According to VGC, Sony is planning to turn Horizon into a trilogy— Nibel (@Nibellion) April 24, 2020
Horizon Zero Dawn 2 shifted to PS5; described as "gigantic" with more freedom to explore and possible co-op mode
Possible standalone co-op game coming that carries progress over to HZD2https://t.co/DhrkWlIEx2 pic.twitter.com/tIQYNcvFQQ
I can see the reason they are ported the first one to PC, is to attract others (PC player) to play the sequel on consoles (PS5) beside selling more copies (just my theory ) . There is possibilities they will make the sequel exclusives.