TPWD says the motors have to be titled. Why, so they can tax you for it and make money on registering it.
I personally do not have my mud motor titled, I have the MSO if there is ever a question of ownership.
My boat is registered and titled, been checked by State and Federal Gw's in different states and have never been asked to see a title for the boat or motor.
If my rig, boat or motor ever gets stolen I do not want it back anyway, I have insurance. Even if it gets stolen you would not need a title to recover as long as you have the serial number and can prove ownership, IE mso, bill of sale, or receipt.