I take it that you missed the part where each companion has their own unique agenda. Just because they are grouped with you doesn't mean they are going to take care of you.
One can also argue that they should be pragmatic enough to not allow you to drag the entire party into trouble just because.
The fact that they currently don't is probably due to the assumption that you can split them up at any time, so it'd be weird to have them contributing to skill checks when they're halfway across the map. But this is probably the only possible advantage to using the chain system to bypass that sort of thing, chained companions should assist in skill checks because if they're too far from each other, they can't be chained to begin with.
Granted, I'd rather chaining be done away with entirely, and allow all party members to contribute if they're within a certain distance.
