Question

why does the term matrix not always fit for every cell type when talking about the Cytoplasm?

Answer 1

matrix is a part of mitochondria ,not cytoplasm.

Answer 2

In cellular biology, matrix or matrices is a description given to structures, which can pertain to a particular part structure or several of its parts. It is not limited to mitochondrial internal structure however. The reason Cytoplasm doesn't hold this description is because it generally has no certain structure or parts of its own. Think of it as general label used to pertain to the "soup" in the cells in which organelles are suspended.