Nobody likes surprises
What car are you more likely to keep? (be honest)...
The one your wife bought for you and you saw for the first time wrapped in a big red bow in the driveway?
The one your wife bought for you after she took you car shopping, had you test drive your top contenders, let you pick out your favorite color, and then drive it off the lot?
Getting leadership to greenlight your product idea works the same way.
Taking them along for the ride is less exciting but far more persuasive than a surprise.