It would appear that Boeing had a small oversight. Building a plane is not like building a car. There are different requirements. While some requirements overlap there are clear fundamental differences.
Now, with that said, it could be that SpaceX and Tesla were allowed to focus more on batteries while Boeing had to improve jet engine efficiency as well as electrical battery usage.
SpaceX and Tesla try to keep as much of this in-house as possible, so they can maintain full oversight and make changes without unnecessary cost overhead.
Boeing had 10 layers of contractors involved in this SNAFU.
WWED = What Would Elon Do.
In this case it is pretty pedantic I'm afraid. Engine subcontracting is pretty standard in aviation. Nearly all of the engine types I can think of are either GE or Rolls-Royce.
It's kind of like Rotax for motorcycles and Snowmobiles... give the designs or specifications to a supplier and have them do all of the heavy lifting.
Now, with that said, it could be that SpaceX and Tesla were allowed to focus more on batteries while Boeing had to improve jet engine efficiency as well as electrical battery usage.