They do. They say every day that "this evolved into that". They just don't put the word "fact" in there.
The fact of Evolution is explained by the "theory of Evolution". Neither Evolution, or the theory of gravity, or the theory of nuclear attraction will EVER "graduate" to "fact".
You are confusing the common meaning of the term with the scientific meaning.
Evolution is both a theory AND a fact.
In rudimentary logic those to thoughts cannot co-exist. If I drop a ball, it falls to the ground EVERY time. It is a fact and the term used for that manifestation is gravity. No one disputes that fact. What we are lacking in the "theory of evolution" is a reproducible "fact" to place it in the same category as gravity.