It's probably my favorite part of HN, at this point. The reaction from people the other day when Google/Apple admit to cooperating with FIVE-EYES was priceless.
Expect another one of those once it gets revealed that marketing/analytics providers (whose spyware litters every single mainstream website & app) are also compromised by intelligence agencies.
There are systems designed to be federated, like email, mastodon, matrix and SMS/RCS.
Signal, WhatsApp, Slack, and iMessage are examples of services which were designed to be run by one company as part of their product. They _might_ have certain SDKs to extend that service (like bots for slack, or app extensions in iMessage) - but generally they aren't excited to shoulder the additional cost and support headaches of third parties using their infrastructure or arbitrarily interacting with the official software clients.
I don't know exactly what you mean by "ecosystem" - I'd argue the first set form ecosystems, while the second set form products.