Boeing Co. limited the role of its own pilots in the final stages of developing the 737 MAX flight-control system implicated in two fatal crashes, departing from a longstanding practice of seeking their detailed input, people familiar with the matter said.

As a result, Boeing test pilots and senior pilots involved in the MAX’s development didn’t receive detailed briefings about how fast or steeply the automated system known as MCAS could push down a plane’s nose, these people said. Nor were they informed that the system relied...