To give an example of why there might be so many tables, here's a few of the variables that must be taken into account, either as inputs or outputs:

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-The weapon you're using

-Type of Shell (different shells have different amounts of drag, and fly at different speeds for the charge.)

-Range to the target

-Relative altitude of the target

-elevation of the artillery piece. (This changes the impact angle of the shell. By varying the speed of the projectile, there are multiple possible angle solutions.)

-Amount of charge. (Artillery has separate shells, and charges. The more charges, the faster the shell moves, and the further it flies. Mortars have 'increments', which work similarly.)

-Time of flight

-Ideal fuze setting (fuzes are used to detonate a shell just barely above the ground. Sometimes this is done through timing, modern fuzes can directly calculate altitude.)

-Maximum altitude of the shell (useful to know for a lot of reasons.)

-Absolute altitude, pressure, humidity, all of which affect drag.

-Winds at altitude.

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To create these tables, you're solving many differential equations, which are non-linear. Non-linear means that it's inaccurate to interpolate an answer. A very small change in initial conditions, may create a completely different result. The more tables you have, the more precisely you can provide the inputs, the better your answer will be, and the more accurate your weapon is.

Now, of course, a modern calculator/portable computer could probably calculate all of these in closed form on the fly, but tables work, they're still accurate, they're straight-forward to troubleshoot. In many systems with severe consequences to failure, there's a resistance to changing anything that works well, especially when the supposed improvement has significant adoption costs and even unknown, unpredictable imperfections.

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