system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does facebook need two apps, one for messenger and one for general use?
gpt
Because messaging used to be a secondary product. The primary Facebook usage used to be the status updates, commenting and the stuff. People were active Facebook users who went to a website, entered their passwords and logged in, played games - and then, used the messaging function at the bottom right. The rise of IM services like WhatsApp made people realize that it was far easier to just message without jumping through all those hoops. Not to mention, Facebook isn't as exciting or popular as it was 5 years ago. It isn't an organic network of friends like it said on the cover. It is mostly an RSS feed of your favorite bands and shows and people. People don't post anymore. Nobody is going to all that trouble of logging into the entire Facebook (both the website and the app) just for messaging which is just text. 

The competition started including additional features like stickers, calls which was not possible to include inside the Facebook app. So they made the smart choice of making it a seperate app that allows them to use it as a distinct developement platform for making bots, turning into a money transfer service, and a formidable communications app in itself. One tap and you cut directly to the chats. No noise like status updates and comments here.