Yes, but in order to be a streamer you have to be successful. As you say, people who play poker, and I would add sports betting, can take it as a job but today if they start from scratch it's going to take a lot more time and effort than it did 10 years ago. The normal thing is to start learning while doing other activities, such as work or studies, and when you see that you are progressing and earning more money there is a moment when you can consider becoming a professional and dedicate yourself to it. Being a streamer, or influencer, is an addition to the income from the game, because what you earn by broadcasting, making videos or advertising is extra income.
Moreover, becoming a streamer isn't that simple; set aside whether or not someone is successful in gambling. There're literally tons of streamers out there; why would anyone watch you? Are you capable of providing something different for your audience, or are you just like anyone else? It's the exact same thing when everyone thought they could suddenly become a YouTube content creator, providing generic content with no diversification.
You can become a professional gambler; does that mean that you should? The majority of us ultimately lose money from gambling; an even smaller percentage would be capable of turning it into a profession; it would require an abundance of time to analyze sports betting because that field is supposedly based on knowledge as well, and even then, there are certainly no guarantees.