Why would Boeing be under review if crew-error is determined to be the cause?
In aviation (and other safety critical areas) it's not enough to just look at the first cause of an accident, you have to look at why that mistake was made, and why that thing happened, as far back up the chain as you can. Then you try to address all the problems.

So, when a pilot makes a mistake, it's tempting to say "the pilots was an idiot. Case closed." However, then you've got to wonder why the company employed idiots, and how many  others are flying. That implies that there's something wrong with the pilot licencing and testing rules, and that has huge implications.

If we assume that these pilots weren't idiots, we have to ask why they made a mistake, because other good pilots could make the same mistake. Anyone who has played a computer game knows that mistakes are inevitable when you're under enough stress, just like a well built bridge will still break if it's overloaded.

You could conclude that they hadn't been trained well enough, which raises the question "Why?". Apparently the pilots did all the required training, so maybe the training was at fault. But it's not enough to just improve that piece of training, you've got to ask why again. Was it not checked? What else hasn't been checked properly? How do we know that any future training will be properly checked? Also, what incentive did the person writing the training have to miss things out, and does it apply elsewhere?

If you don't find and fix the root of a problem, it will continue to grow until it pops out somewhere else and causes another tragedy.