If a misaligned AI escapes containment even once in the entirety of humanity's future, there is a big problem.
It sounds like your model of AI usage assumes we will also have a perfect ability to contain any AI developed anywhere in the world, under all conditions, for ever (or for as long as there are computers).
The AI risk argument says we should take seriously the possibility that we may not be able to maintain a perfect 100% success rate on that.
I haven't suggested anything that is physically impossible - merely things that are improbable and hard for humans to achieve. It is hard to foresee all of the possible avenues for escape, let alone ensure that they are all closed under all possible future states of the world.