I was on the beta testing team and have been using Beeper for a little over two years now.
The convenience of having an application to house all of your chat networks is amazing.
Once everyone ran around with smartphones using WhatsApp, fewer and fewer people cared about MSN, ICQ, etc.
People moved around, but often still use several apps even today. You might have a “main” app you use with friends (this used to be MSN Messenger for me back in the day; now it’s Facebook Messenger), but there may be other people you chat to that use other apps. Facebook Messenger, Whatsapp, Wechat, Viber, Signal, Telegram, Slack, Discord, Skype, Kik… I feel like there’s actually more major apps today than there used to be.