The hard tyre wasn't the problem. Ocon's pace on it was faster than Leclerc's — and Leclerc was managing tyres to the end while fighting for the win. If Alpine had left Ocon out, he would have finished comfortably in the points with the pace he had. Instead, they bolted on softs with four laps to go, as if track position didn't exist.
The only explanation is that Alpine looked at their own degradation model, saw something that wasn't there, and reacted. Meanwhile, Ferrari — and everyone else running a one-stop — trusted what the tyre was actually doing. Ocon's race average on hards was over 100 seconds. Leclerc's was under 99. The hard tyre worked. Alpine just didn't believe it.