Subgroups are those that have as a foundation the books known as the Bible.
These are Judaism, Christianity, Islam, and Baha’i (in order of historical foundation) all of whom treat the Bible as sacred. There are at least 6 other Abrahamic religions including the Druze.
Why categorize these groups together? Because the majority of the world’s religious adherence is to these religions. All other religions are grouped under different headings, depending on their beliefs.