Didn't they start with xmpp? Going from nothing to an established standard gets you going quickly, and then modifying that past the point of compatibility is a reasonable (if potentially cutthroat) business decision. Going from a custom standard to an established standard seems to signal that they actually want to embrace it, though of course doesn't rule out that they also want to extend/extinguish it later.

The internet was a different place back then.

Everyone, especially regulators, have seen on many occasions now what vendor lock-in looks like and the benefits of open standards.