The single largest cause of the type of failure the OP describes is shifting under load. This twists the chain and forces the plates outward on the pin and will break any chain. It doesn't necessarily break during the shift, but with a plate hanging on the edge it'll break the next time it's heavily loaded.

To prevent this type of failure modern chains (since Hyperglide) have the pins peened over the outer plate forming rivets like those used in bridge construction. This is why they cannot by cut and spliced by simply pushing the rivet back and forth. Once the peened lip (think rivet head) is sheared off pushing the pin through, there's nothing left to prevent plate spread when the pin is pushed back.

Getting back to Sram- Srams chains come in a range of qualities. I suspect that the basic parts are the same differing only in finish, but the biggest difference is the type and extent of peening of the pins, running from 4 points at the lower end, to 100% at the top. The greater the extent of the peen, the greater the resistance to damage from shifting under load.

Note that all chains meet the same standards for break strength under tension, and if not for side stress all would be equally strong.