There are definitely good, non malicious reasons to have it as a separate app and that should actually be preferred. Off the top of my head:

• Separation of permissions - it only has the permissions it asks for instead of every permission messages has
• It can be disabled/removed without disabling messages
• it can be reused by other applications if that’s a desirable feature

Some people might actually like this: thinking of women getting unsolicited dick picks in particular