Do you actually have a decent following on Twitch? Are you able to pull those people into your YouTube platform? You don't have to relegate yourself to a single platform, but it will involve using strategies that cater specifically to them. If your Twitch followers don't respond well to a simple call-to-action to follow you on YouTube, then you might want to consider sticking to a single platform, knock that out of the park, and then start spreading elsewhere. Consider the time commitment needed for each.