All artists would love full creative control over their work at all times. Unfortunately when your creative pursuit also is your job, sometimes you need to think more practically. This is something I've struggled with as I've tried to find a niche with my writing while emphasizing my strengths. My writing is much more than a hobby; it's a part-time job for me right now, with the hope of it someday being my full-time job. As such, I look at markets where I'm able to utilize my strengths in a way that will perhaps also be a good move financially.
Some writers I know resist this. They don't want to turn their creative outlet into something that can be readily changed at whim to fit a certain market. It doesn't bother me at all because I look at my larger objectives and try to ensure that any project I take on fulfills most of them.
Every writer has particular skills that set them apart. An ear for dialogue, for example, or a descriptive, unique style. Even if the market you've chosen for your work isn't necessarily known for those attributes, it's important to always put your own stamp on each piece of writing you submit. Your author voice is what a reader will look for, even if you change genres or lengths or whatever the case may be. Your personal signature is also what will set your writing apart.
For example, I mostly write erotic romance, as do many other authors. But I think I bring a sort of snark or sarcasm to my work that maybe not everyone else does. Some may love that, some may hate it, but it's an intrinsic part of my voice and carries over into every piece I write. And even though the characters will change and sarcasm may not always be appropriate, I try to make sure my voice is front and center in whatever style of writing I'm doing that day. It's also a way to kind of write to the market while still maintaining your own integrity, in my opinion. You may decide to write something way outside your normal realm of interest because it seems like it may be profitable, and there's nothing wrong with that. Your talent is yours to do with as you see fit. But making sure you insert your own little tells, or the kind of things that really bring you joy when you're writing a story, is one way to always make sure you're fully invested in every story you bring to the table.
What about you? Do you believe writing should remain an "art" or do you write things you might not normally to see if it will be financially profitable for you?