Others can be really personally attached to a few niches because they find them highly fascinating. And of course it's usually not only one or only the other. Some lean partially one way or the other
I personally have a few niches I'm really attached to and comfortable with, and anything else gives me the subtle sensation of being kinda lost. Partly because I find market research to be a little confusing. I'm still learning the basic ins and outs.
My favorite niche. is martial arts because I've been learning it myself for years and It's very familiar. I have a natural fascination with it.
But I really need to really check myself to be sure I'm pitching from someone who doesn't share my background and perspective.
A mistake many beginning copywriters make is that they don't think they have enough experience to start an actual paying project. And it's kinda that way with beginning to learn anything. It's easy to be doubtful and hesitant.
It's important to recognize the fact that any subject you're already familiar with is something you can confidently write about, and therefore turn it into some income. And it doesn't mean it will be easy. It doesn't mean you have to do everything yourself(part of being a copywriter is gathering feedback). It doesn't mean you can quit your job in a month. But you can do something. And that is the best way to really get the learning rolling