Akiva,
The problem is that Rav Kanievsky’s position is contrary to what the common practice seems to be. It’s one thing to say “cover the bases” when it costs nothing extra or when it’s possible to do all options. However, here, you can be faced with a dilema:
It’s near Mincha time and you don’t have a hat/jacket. There is no time to get your hat/jacket and still make the minyan. So, what do you do? Do you daven alone or do you make the minyan?
R. Chaim’s position (as reported) is to daven alone later with your hat/jacket. Most of the world seems to take the opposite approach. The two, however, are mutually exclusive, which does not fit into Pascal’s Wager.
The Wolf
(Of course, Pascal’s Wager has a HUGE flaw in the logic, but that’s another argument for another time.)