It follows from Turing completeness. See https://en.wikipedia.org/wiki/Turing_completeness. It takes very little for a system to become Turing complete. And once it is, you can include arbitrary computations. Proving that they stop is impossible in general due to the well-known Halting problem.
https://beza1e1.tuxen.de/articles/accidentally_turing_comple... offers examples showing how easy it is to accidentally get Turing completeness, including multiple widely used type systems.