After having a testing round in Thailand and Australia, Facebook has decided to take the ads on the Facebook Messenger home screen worldwide. Before the end of 2017, you will most likely see the flow of your home screen broken up by sponsored ads. Just like that the ads you see on Facebook itself and Instagram will be targeted and specific to you.
Aside from the home screen placement, businesses that are using Messenger as a platform can already send sponsor messages to users that have messaged their business before. Advertising is not necessarily everything, but it is definitely being treated that way, but it is a way of making money right now in today's digital day and age.
The Facebook Messanger home screen will slowly start filling with adverts, so maybe if enough people end up hating them, Facebook will stick to its other platforms and leave Facebook Messenger as is.