Why is it never-ending?
Because Pi is an irrational number.
In the late nineteenth century there was a debate in professional math circles as to whether every number was the solution of an algebraic equation. The matter was resolved with a proof that pi is not such a number. Another transcendental number is e (~2.7182818284...), the base of natural logarithms and there is also the Euler-Mascheroni constant (~0.57712...). Any rational multiple of a transcendental number is also transcendental so there are a lot of them.
Because Pi claims to measure a “circle”, a thing that does not actually exist. What exists is a series of connected triangles.