Streaming can be very stressful if it is your only source of income
1) Requires significant time investment to be successful in most cases, especially when you include the stuff beyond the actual stream (promoting on other platforms, etc)
2) You're basically an independent contractor. Unless you've signed with an agency that will provide you with various "employer benefits", like disability and medical, you're very vulnerable in the event something bad happens, like you get sick or injured
3) Income stream can be very fickle, so in that sense it can be more akin to a commission-only sales job. It makes it very difficult to plan for the future, since it can be very boon & bust. This can also impact your ability to secure favorable loans or mortgages. Uncertainty = stress
4) Boredom/lack of motivation/burnout: This isn't unique to streaming obviously, but it has the same stressful impact on a person. If you aren't enjoying what you are doing, but feel forced to do it because it is your income stream, that can be very stressful. This strongly impacts those streamers where their audience is basically contingent on what game they are playing and they feel forced to play it to maintain the income stream.
5) Hecklers/Trolls: At some point, the chat telling you that you suck at a game, or are doing something wrong, or should be doing something else, or just being trolls can get to you