There was not a "very high" chance of another off in the same spot. It's extremely rare for F1 cars to have incidents in the same spot, yet alone in such a short space of time.
Very high is both one, not a number but comparative( 5% chance would be considered very high risk when talking about motor sports, yet low chance when considering winning on a scratch card) and anyway, you're wrong. There is a high chance of an off at the same spot.... read this important bit, IN CHANGING CONDITIONS. Drivers don't know about aquaplaning till it happens, when the track gets enough water and the drivers can see it for the first time they are 1 second from driving through it, it's too late.
In dry when someone goes off it's a driver mistake, car failure, something, and yes the chance of going off at the same point is pretty ridiculously low and it relatively rarely happens. In rain as conditions approach aquaplaning levels then it happens significantly more often. If cars go off at the same place 0.05% in the dry and 15% due to aquaplaning then that is both very high and absolutely not worth the risk of putting out a tractor/truck/whatever in that path.
Look up on youtube, there are dozens of video's of multiple cars going off in the same corner over and over again in the rain. Rain ENTIRELY changes the chances of things to happen, to the point where putting out a dangerous vehicle without making the track significantly safer with a safety car is completely negligent.
It wouldn't matter if it's a 5% increase, that is statistically huge. But there are so many races where changing conditions has caused loads of drivers to go off and often at the same points. Aquaplaning is not a car failure or driver error, it's something the cars simply can't deal with and can catch out anyone very easily.
The fact that there are video's of f1 cars hitting tractor/similar vehicles from aquaplaning in the rain should suggest that it's not something that never happens.
In more races than I can remember when rain comes in drivers frequently go off on the same corner as rain tends to hit one part of the track first, catching a lot of drivers completely unaware.