Part of the answer is the "magic" of matrix math. You can represent multiple linear equations in every row of a matrix and when you apply one operation (add, multiply, etc) you performed it on all your encoded equations inside the matrix.
If you can, for example, represent your problem in a linear equation (algebra) then you can also formulate 50 similar equations. You want to "transform" all your equations by some operation (lets say divide by 20), so instead of calculating 50 times that operation for every equation you just do it once if you encode them in a matrix.
This started in graphics when you wanted to apply the same operation to many pixels on a screen (i.e. apply a shading rule), so that's why video cards have these massive processing power on pixels.