Here's why:
* Suffixes are added to the end of a word to change its meaning or grammatical function. "Mental" would typically be a suffix indicating a state or quality, like in "fundamental" or "sentimental."
* "Governmental" is derived from the word "government," which is itself a noun. The suffix "-al" is added to "government" to create the adjective form, meaning "relating to or characteristic of government."
Therefore, "mental" is not a part of the word "governmental."