Note that it's not just "maybe there is randomly some new heavy element that's stable out there". We see definite hints in the behaviour of known heavy elements

Note that it's not just "maybe there is randomly some new heavy element that's stable out there". We see definite hints in the behaviour of known heavy elements, and in our best models of nuclear physics, that point towards a possible island of stability. https://en.wikipedia.org/wiki/Island_of_stability https://en.wikipedia.org/wiki/Island_of_stability