It's because the meanings from the adverbs along with the prepositions generally continue to be precisely the same in these phrasal verbs. For instance, the indicating of “up” in Pretty much all phrasal verbs is connected with ending or completing some thing. Which explains why follow-up letters are made. https://riverjdqex.blogdemls.com/32291017/the-2-minute-rule-for-english-tenses-simple-present-tense