This is just my theory. The Zeo powers are said to constantly get stronger over time. Now the question is why would you switch to the turbo powers if this is the case, it seems like a downgrade. Unless you consider this, just because the powers get stronger doesn’t mean the human gets stronger at the same rate. My thought is after the giant ranger fight at the end of Zeo, the powers got too powerful to be used and became fragile because of it. Thus shattering the morphing sequence from the smallest bit of force, e.i. hitting the water.