The fundamental issue Gegenbeispiel is that any warning would violate or jeopardise the common type endorsement without simulator training with previous 737 family members. Boeing had contracted to accept a $1 million dollar penalty if simulator training was required for some 250++ jets with one operator. It also enhanced the sales pitch with other operators.
Subsequent revelations (Forkner chats logs) have revealed Boeing actively "Jedi Mind Tricked" Lionair into not requiring simulator for their own crews as Boeing were concerned other operators would be influenced to do this for their own crews, leaving the perception for potential purchasers that it was best practice to require training. This would increase the costs, and thus reduce the attractiveness of the 737-MAX relative to the Airbus A32x Neo family.
It was mentioned at one point the cost was about $2000 (assumed USD) per pilot was the cost if a training simulator was required.