First of all, any exclusivity requirements on any platform. Something like this must get you in trouble with the TOS of any of these sites.
Second, the culture of streaming on each platform is unique. Not to mention the form factor and expected behavior of any chats on each system. Or even things as simple as vertical vs horizontal video formats. Sure there are areas where this doesn't matter, there always are, but it shouldn't be ignored when trying to spread your reach.