Why is it that utilizing clockwork motors never came into fruition as power sources for things like vehicles and bolt shooters, in place of compressed air and strings?
The fundamental issue is energy density. A spring simply doesn't store that much energy per unit mass and is ultimately limited by the yield stress of the material.
Where springs are good is in providing large forces over a fairly short range of movement and time so they are good for things which require a fast response.
There area also issues with managing the power delivery of springs as they naturally provide a force proportional to their extension. There are ways around this which have been developed for watches etc but they add a lot of complexity and are difficult to implement for power systems.
Springs are ok for things like watches because a watch is (in a sense) a fair attempt at a perpetual motion machine and work well with motive power which provides a lot of torque but don't need much actual energy.
Compressed air is only a bit better than springs in terms of energy density. It is just about feasible for vehicles in special circumstances eg compressed air locomotives have been used for situations like mines where there is an explosion risk. The advantage of compressed air for workshop tools etc is that it can be produced centrally (with a big compressor) and distributed, also air tools tend to be lightweight, compact and reliable compared to electric ones, especially for high speed, low torque applications like die grinders and polishers. pneumatic are also good for very high speed, compact actuators (F1 cars have pneumatic valves for example).