I often find myself on the receiving end of this question or a variation of this question. The subtext, no matter how kindly meant, always feels like: will you ever write a proper novel. As a question, it's up there with, wow, you're really churning them out aren't you? - although I might have to tackle that one another time.
The short answer is, probably. I like writing thrillers, I get paid to write them and it took me over ten years to get here.
The longer answer is more likely to be another question, something along the lines of: would you ask a fashion designer if they were always going to design clothes, or shoes, or coats? Or maybe ask an architect if they were always going to plan houses, or kitchens, or loft extensions? But no one ever asks those questions because that would be rude. It would be to insinuate that the designer or the architect (or the teacher or the accountant, choose your own examples) have somehow failed in their profession by, in the first instance, not actually becoming Stella Mac Cartney or Christian Dior or, in the second, not achieving the renown of Sir Christopher Wren, say, or Zara Hadid. To ask such a question would be blithely to sweep aside all those years of training, the intense competition, the sheer grit required to turn talent into a paid profession. It would be to suggest that the only respectable, indeed viable outcome for that talent would be global fame and adoration - prizes, second homes, a place in the history books. In the case of the writer, will you always write thrillers? is to somehow imply that becoming a professional writer of suspense novels (one of the most competitive genres in one of the most competitive industries on the planet) is effectively failing in some way - failing to write the quintessential novel of the century; failing, perhaps, to become J D Salinger or Margaret Atwood. And of course, in the shadowy corners of this female psych-thriller author's brain lies the question, would you ask a male thriller writer this question? Would you ask Stephen King?
So back to my short answer: probably. Probably, because when I approach the work of a new psychological suspense, I do so as I would a novel. Because that's what it is. I am paid to write psychological thrillers and so that is what I sit down to write. Avoiding the formulaic as much as I am able, I nevertheless use the tropes of this genre rather than those of romantic comedy or sci-fi: slow-building tension, unreliable narrators, dysfunctional relationships, the reversal, the twist, a pared down list of characters, an atmospheric location, etc. All novels depart from a framework, whether it is by subverting that framework or adhering to it only very loosely - that, along with the tropes, characterization, dialogue and action, etc, is part the craft but these elements are not what interest me most. Psychology, intimate relationships, friendships, community, society, sexual politics, trust, love, frailty, vanity, vulnerability, family, sex, death, how far we might go to protect those dear to us or what, materially, is dear to us ... these are the things that interest me - in short, what it means to be human. When I set out to write a psychological suspense, I seek to explore what is troubling me or fascinating me at the time of writing, often on the back of something conceptual or 'literary'. I'm still telling a story. I'm still trying to reach and enthrall a readership. I suspect all writers feel this way, since we are all packaged in order to be sold, just as I suspect that when all of us sit down to write, we do it as if, well, as if we were writing a proper novel.