Frank
Because if you select Intermediates or Wets in main strategy the game assumes the manager made that setup during rain conditions (and/or that manager expected those to continue into the race). As it isn't raining anymore the game chooses the 'If rain stops use... tyre' as the starting tyre as it now assumes the conditions aren't what expected anymore and the tyre set there is the one to use in case it's not raining anymore and since 'after X laps' is not a valid measure of time before the race even started it ignores that.
The same if the setup uses dry tyres in main and it starts raining, the game assumes the manager made the setup during dry conditions and expected the conditions to remain as such, wrongly as it turned out, and thus the game starts you using the option 'If it's raining...'. As any rain tyre usually is better than any dry tyre in rain it ignores the X mm value.
As said, in the past that worked pretty well except the weather really changed during the few minutes of lock down. But not anymore due to the way slowed down water level changes, although the way it is now it doesn't matter that much because even after rain stopped it's still Intermediates for the next 1-2 hours.
Ok, that make sense. When you made a tactic and stay offline: if the rain starts and stops again during the race; there would be about 6-7 pitsopts. And about your said at last sentence: yes you are right inters. perform well at that situations but it is a bit important selecting fuel load. Still need to upgrade.
Thanks mate i learned a lot.