Meta is a holding company, much like Alphabet for Google, and is intended to limit cross-concern damage. By keeping services as separate entities under the hold

Meta is a holding company, much like Alphabet for Google, and is intended to limit cross-concern damage. By keeping services as separate entities under the holding company they are shielded from each other to an extent with regard to tax, other financial, regulatory, criminal, and other responsibilities, so a massive problem/scandal in one service can have its blast radius more easily managed. These arrangements also make it easier to close things down if needed: it simplifies redundancy (“why can't you offer me a replacement role over there?”, “that is a separate company”) and so forth, though this is more a concern of smaller organisations than Meta & Alphabet. A company I've worked for once had a significant rearrangement with people signing contracts for specific parts where they had previously been employed by the larger group entity, shortly before “divesting” some of those parts. Shady, but legal.