It is important to be broad in the way we define abstinence because the definition can vary drastically from person to person, depending on their experiences, what their values are, etc. In order to properly account for different perspectives, the way we define it must not only be comprehensive, but also ever evolving as we learn more about how other people view it.
Some people might argue that it only counts as abstinence if they completely refrain from sexual activity. Some people may also argue that it’s a more religious or spiritual decision rather than a personal one. While these opinions are valid, ultimately they would be trying to make abstinence fit into the definition they feel suits it best, without fully taking into account why other people would define it differently.