I am trying to remove stop words before performing topic modeling. I noticed that some negation words (not, nor, never, none etc..) are usually considered to be stop words. For example, NLTK, spacy and sklearn include "not" on their stop word lists. However, if we remove "not" from these sentences below they lose the significant meaning and that would not be accurate for topic modeling or sentiment analysis.
1). StackOverflow is helpful => StackOverflow helpful 2). StackOverflow is not helpful => StackOverflow helpful
Can anyone please explain why these negation words are typically considered to be stop words?