Complex sentence: Because of the development time to create and tweak such movements, watch manufacturers tended to enter very few movements at observatory competitions, primarily very specialized movements designed specifically for such competitions and not suitable for actual wristwatch usage.
Split into simpler sentences: Because of the development time to create and tweak such movements, watch manufacturers tended to enter very few movements at observatory competitions. Such specialized movements designed specifically for observatory competitions were not suitable for actual wristwatch usage.