Re: 'Spade' type stick?
I am not a qualified pilot, but I surmise that as these sticks were fitted to manually controlled (ie no power assistance) aircraft and that the dynamic loads back to the stick varied much with the flight regime, such that it may have been felt advantageous to have the facility for a two handed pull or heave, in certain corners of the envelope.
I am sure that far better qualified people than me will be here with a better, concise and more accurate answer shortly.
Conan