I'm not very familiar with Twitch, but isn't the community interaction (text/voice chat?) a large component of it? I'd imagine these streamers would be very interested in chatting with the 1 or 2 people who stopped by their stream.

If the bots can't respond they'd be found on pretty quick, and making bots who can pass some sort of "video game specific Turing test" is a major endeavor. Only getting instantly recognizable fake viewers would as demoralizing as no viewers.