[asteroidbelt]

> You can post on FB about Twitter or Mastodon

Because people do not threaten FB to leave to Mastodon. But you can't link (maybe you can now, but some time ago you couldn't) to Telegram inside Whatsapp, because Facebook considered Telegram a competitor.

> You can search on Google about DuckDuckGo

Again, because Google does not consider DDG a competitor.

But a while ago (long before the war when everybody were at peace), Russia was the only country where Google Chrome did not offer the choice of search engine. Because Russia was the only country where Google was not the leading search engine. There's famous commit in Chromium repository which explicitly excludes Russia.