"Boeing" is not a cause. Things like their safety culture can be a cause, or lack of good process control can be a cause. The reason why Boeing is catching a lot of flack is because they deviated substantially from best practices. This is related to your other comment so I'll just respond here.
There is a general hierarchy when it comes to controlling hazards (remember, Boeing already identified MCAS as hazardous): remove the hazard, engineering controls, administrative controls, and PPE. We can apply a little thought experiment to see the gaps in what you're advocating when it comes to the MCAS issue. (Admittedly, this is contrived to just illustrate the point within the confines of a forum reply).
1) Remove the hazard: They could have redesigned the airframe to adjust the center-of-gravity to remove the stall issue that MCAS was developed in the first place. Why didn't Boeing do this? Because of cost and schedule pressure to have a new plane ready, after threats that American Airlines would take their business elsewhere.
2) Engineering controls: MCAS was an engineering control, but an incomplete one. Because MCAS was listed as "hazardous" in the hazard analysis it required redundant sensors. Why didn't they put on redundant sensors as the default? I can only speculate, but considering they were sold as optional, profit motive seems likely. (This also ignores the fact that MCAS should have been categorized as 'catastrophic' meaning they didn't fully understand the impacts of their system)
3) Administative controls: this was the training piece that you're hanging your hat on. This has multiple problems. For one, even though MCAS changed the handling dynamics of the airframe, Boeing pushed hard to reuse the same certification to avoid additional pilot training. Again, this was a business decision to make the airframe more competitive. Secondly, administrative controls are an inherently weak because of human factors. There's a lot that can go wrong if your plan is to have humans follow an administatrive procedure. You claim "it's not hard". Sorry, this is just a bad mindset. Usually when I hear people say things like "it's not hard" or "all you've gotta do" when they're talking about complex systems, it indicates they take an overly simplified mental model. In this case, you may be ignoring the chaos in the cockpit, the fact that the plane has handling characteristics different from what the pilots were trained on, human factors related to stab trim force at speed, conflicting or confusing information (like why the MCAS comes on at changing timeframes, time criticality, etc. Having adminstrative controls as your main mitigation is bad practice, and setting the system up for failure.
4) PPE: this isn't particularly relevant to this case, but a silly example of PPE control is giving everyone parachutes and helmets in case things went south.
You can obviously see PPE is an absurd control. But your main point is that the main control should be administrative, which is the next worst option. Boeing ignored good safety practice to pursue profit. So they probably deserve some of the heat they are getting.