Here's why:
* Suffixes are added to the end of a word to modify its meaning or grammatical function.
* "Competitor" is derived from the Latin word "competere" meaning "to strive or contend". The "or" ending in this case is a common suffix used to form nouns that indicate a person or thing that performs a specific action.
Therefore, "itor" is part of the root word and not a separate suffix.