Most of the time, this kind of "exodus" happens because the business somehow mismanaged their employees which resulted in them not being happy, leaving the business and opening up a new one.

Even then, if I knew my business would be superior, I wouldn't mind that much. In the case of repl.it I don't see any reason why Riju would pose even the tiniest threat. It's super basic with no obvious plans to be compete with repl.it. Just look at the polish of both products, one is a serious business with funding secured while the other one is a small OS web-app written by somebody in their free time.