Answer:
Because have in "I definitely have no friends" is used as main verb and not as auxiliary/helping verb. And, "I definitely was not at home" is more correct than "I was definitely not at home"
Explanation:
Usual position of adverb definitely (which is an adverb of certainty) is after auxiliary/helping verb and before main verb.
"I definitely was not at home" is more correct than "I was definitely not at home". The first sentence conveys a sense that I was not at home, with stress on I and no clue or stress on wherever I was. However, if the speaker wants to put more stress on location/place "not at home but somewhere else" then second sentence ("I was definitely not at home") is better. It conveys I was not at home but somewhere else.
