but an instant messaging client is something pretty simple that it doesn't take hundreds or thousands of engineers to get right and make into a good product.
While you are technically right, making a good (as in "usable") chat client takes at least a competent developer and a UI designer, and most OSS developers lack in the second domain.
Especially for XMPP, you also need to apply a number of extensions to improve the experience.
From personal experience as an XMPP client developer and XMPP Standards Foundation member I can say that most of the work is driven (slowly) by volunteers, and that there is more work than time. We are starting to cover the UX side of things to make XMPP easy enough to compete with WhatsApp, but we need YOU to contribute. ️
While you are technically right, making a good (as in "usable") chat client takes at least a competent developer and a UI designer, and most OSS developers lack in the second domain.
Especially for XMPP, you also need to apply a number of extensions to improve the experience.
From personal experience as an XMPP client developer and XMPP Standards Foundation member I can say that most of the work is driven (slowly) by volunteers, and that there is more work than time. We are starting to cover the UX side of things to make XMPP easy enough to compete with WhatsApp, but we need YOU to contribute. ️