> I suspect there was no enterprise level push for XMPP anywhere.
At the about the time when federated XMPP could have gained momentum at the enterprise level, 2005-2010, SaaS and then cloud began to take off. Enterprises began to shy away from hosting their own services. Even though many were still hosting their own e-mail and web servers, it was already too late for XMPP, especially given all the other factors--IM wasn't yet a killer business app, etc.
Without a large, diverse group of players effectively forcing federation, there was nothing countering the incentives for big players to create walled gardens.
I worked at company, Barracuda Networks, that acquired an enterprise XMPP appliance product around 2005. They also hired the main developer of one of the most popular open source Windows XMPP clients to help them integrate enterprise features (LDAP, etc). After a few years they basically put the project on life support. If there was more enthusiasm, and Barracuda worked harder with other vendors to build a large installed base, improving the overall value-add and "creating" a market, maybe things would have worked out differently. But that's a big ask for a bunch of medium-sized, short-term profit-seeking companies. Eventually startups like Slack ended up doing something like that, but using proprietary, walled-garden, hosted services, a model where they could capture entire markets--i.e. a big enough potential pay-day to make it worthwhile. :(
Another alternative scenario: maybe if anti-trust regulators came down hard on Google when they began to close-off federation. GTalk could have been (and briefly was) an important anchor tenant for a nascent federated IM ecosystem. Not sure it would have been legally viable, though, to restrain Google that way given the state of IM at the time.