Only having one style in art is similar to only being experienced in one specific field when it comes to the market.
If a specialist is searched for and your style happens to be the sought after speciality, you're in luck.
It's just way more difficult to find clients if you can only offer one type of service.
I've seen a few artists who fancy a variety of styles either because they like to experiment with style or because they know learning different style will broaden their market opportunities.
It's really hard to open up yourself and try something out of your comfort zone when it comes to art, because many artists have a very personal attachment to their style and don't want to sway from it, because it feels like betraying yourself. It's not wrong to stick to a very personalized style, but I have mad respect for artists who constantly leave their comfort zone and surprise me with something I never would have expected to see from them.