This isn't well known, but to monetize on Twitch (i.e. be able to receive subscriptions and bits), you have to sign an affiliate agreement[1], which includes a clause prohibiting you from multi-streaming, or putting your VODs up anywhere else for a full day after their conclusion. This severely limits your ability to cross platforms.
One is taken for granted, but I think it is a valid point. I share your opinion (bad to depend on platforms), but that never might have triggered the comment.
For some people never means usually not, and for some never means never :)
[1]: https://www.twitch.tv/p/en/legal/affiliate-agreement/