It's a minor adjustment, but it's most likely a move to make Messenger more like Whatsapp in terms of texting and calling. To call a friend before the update, users had to establish a separate chat thread with them. The new feature allows users to call friends directly and may act as an introduction to Messenger's calling features for those who are unfamiliar with them. Facebook Messenger has been one of the most popular videos calling apps throughout the pandemic. Because of the increase in audio and video calls, the decision to integrate calling on the Messenger app's main screen was made.