Everything is encrypted in transit, under ssl. P2P encryption however required device to device connection and usually only used for one to one messaging or very small groups (ie using Signal protocol that creates multiple entry to end connections to enable encryption) and is not technically possible for a web-app. Device must be signed using native app. True p2p encryption is what you see on something like Signal or Telegram apps but not on FB messenger for that very reason.
We choose to focus on integrated community experience where chat is a part of web experience, so at this stage end to end encryption is not feasible. We have to choose our battles and our approach is to enable more niche communities to appear and let people network around specific interests or affiliations. When it comes to software for sensitive communication that must be end to end encrypted, this problem is largely addressed by Signal, Telegram, et al (not so much WhtsApp due to questionable meta data privacy tactics) so we can focus on community networking.