Glad to see this case here. I've been reading about it ever since it started hitting MSM a couple weeks ago.
There is a book, Deep Survival: Who Lives, Who Dies, and Why by journalist Laurence Gonzales. Highly recommend for anyone who does outdoor adventures as well as anyone who sleuths outdoor adventures gone wrong. I learned a lot from this book about how there are some mental constructs that we need to be aware of and actively combat in order to stay alive. For example, the "We've already put in X hours, we can't give up now" and the "Just one more (mile, hour, turn)" are two thoughts that are very common and get people into a lot of trouble. Also, the "Just going out on a quick hike,, no need to take snacks/water/a jacket" until the storm rolls in, there is an unexpected detour on the chosen route, and someone twists an ankle. He presents a list of rules, including "If you planned to leave at X and get delayed, do not continue with the hike." and "Every person needs to have their own map and communication device/gps beacon."
At any rate, I highly recommend the book.
My guess (not an expert in any high-risk adventure sports, so just my opinion!) is that this has a lot to do with ego and them getting in over their heads and him not being willing/able to make proper choices once things started going south. He was the experienced hiker, and when (if) she started questioning him or wanting to turn back, he wouldn't, and managed to convince her to keep going. Or perhaps she was too caught up in also showing she was strong and capable (his equal) that she mustered on long before she should have stopped.
This is a case I hope is recorded, or there is a good reporter texting from within.