As large, centralized companies come to dominate the internet for most users, they become choke points for censorship. (Please don't call them "cloud" anything — the real cloud is in the minds of the people who use that term.)

In the free world, we do not depend on those companies, or any specific companies. That is necessary for freedom.

Note that Telegram's cryptography software is not "proprietary" in the usual sense; the Telegram client is free software. WhatsApp, by contrast, is proprietary software, which is plenty of reason to refuse to run it.