stable is called stable because of stability

stability
noun [ U ]
uk
/stəˈbɪl.ə.ti/ us
/stəˈbɪl.ə.t̬i/
C1
a situation in which something is not likely to move or change:
a period of political stability

The point of a stable distro is that it’s unchanging. That way you have predictable issues that you can solve in the same way for the lifetime of that version.

Reliability is a side benefit of maintainers choosing the best available version to freeze.