A lot of artists ask me for career advice. One of the first things I usually do is ask them to show me their work. When I ask to see their art, often they're expecting me to critique it like in art school. Critique the colors, the technique, the composition of individual pieces. But that's not what I do. I look at all their work as one body of work. What I'm looking for is simple - can I tell all this art was made by the same artist? If the answer is "No" - that's not good.
This is a hard pill to swallow for a lot of artists - what your style is, is really not that important - what's important is that you have one! When you're trying to sell art, long term, it's really important to have a style people can recognize without even needing to see your signature - a signature style. If you're making art in different styles, and always trying new things, you'll have a hard time developing a signature style. That signature style is SUPER important - I can't stress that enough. If you want to earn a living as an artist, you're going to have to narrow down a style, at least until you're making a living full time.
You don't have to create the same thing over and over - that's not what I'm saying. What I'm saying is, in your unique way, make a thread that somehow connects all your art. It can be as simple as sticking to portraits, or landscapes. It can be as simple as "why does she always have that weird red blob in all of them?" You can try different mediums for sure - just don't forget that red blob. If you're painting landscapes one day, and portraits the next, then trying different styles of abstracts, it can confuse the viewer AKA the potential art collector. You don't want to do that.
The truth is, in the art business (and it is a business) generally 80% of your sales of original art will come from 20-30% of your clients - the ones who collect your art. Art collectors generally won't admit it directly to you,but, when they buy your art, they hope it will increase in value. If they're presented with a jumbled mishmash of different styles from the get go, they won't know which one to invest in, they won't know which one you'll be best known for in 10-15-20 years. And instead of buying a lot of your different art, they'll buy none and find an artist with a signature style.
Another reason is simple - they want things that match. In interior design, matching design elements are important. If you develop a style, you might sell 7-8 pieces at once! I have. It also makes it a lot easier to get into those ever elusive reputable galleries.
Galleries understand the art business - or they go out of business. So, they almost always stick to showing artists who have a style. Just like individual artists, galleries make the majority of their sales to a relatively smaller % of their clientele. Art gallery clients usually don't want a deal - they want a good investment. If you don't have enough art in one style to fill the walls in a gallery, they're not very likely to give your hodgepodge of work their valuable space and resources to set up a showing of your work. Because their clients won't know what style to invest in, and they won't buy anything anyway.
This is why it's important to create what you love! If you're having fun making art, then you'll create more of it,and have more chances to really develop that special thing that uniquely defines your art. If you simply can't have fun without doing radically different things, then you can make different styles to your hearts content - just don't share them with people, stick to sharing one style for your "career" art.