Why early screw ships lacked folding propellers

Why did early screw-propelled ships not simply use folding propellers?

Because the mechanism had not yet been developed, and too few propeller-driven ships existed to create the engineering attention and demand needed to solve the problem quickly.

A viewer asks why early screw-propelled ships did not simply fold or retract the propeller. A solution that seems obvious in hindsight still had to be invented, engineered, and justified by enough operational demand. When only a few propeller-driven ships existed, relatively few people were working on their special problems. Adoption gave the technology a larger community of users and designers, which made later improvements more likely.