I guess he was only 1 lap short of the tyre lasting, and perhaps hadn’t felt comfortable on the medium in practice.
The retrospectoscope is a powerful instrument but you would have to think on form all year that he would be faster than Zarco who won on the same tyre, and PI is pretty much known for being abrasive on tires, so a soft tire strategy pretty much was a significant gamble.
In my view in this and the last race he hasn’t looked at any strategy other than going all out to win both races. Sure that is how he got to the lead in the title, but he also did this due to mistakes from Bagnaia, and once in the lead he could perhaps have been more strategic, which I had thought after the previous race as well, leaving the pressure on Bagnaia, whereas now it is all on him. I guess MM has been known to make a soft tyre last when nobody else could, but even he also eventually evolved to being prepared to take a podium result rather than going all out to win in the interests of winning a title.