Writing promotional copy for a product is sometimes fun.
You get to hype the product using vibrant language, and if you actually like the thing you're writing about then it's even more fun!
But, regardless of how you feel about any subject, the body copy should emphasize the benefits for the end user: what the app does, why it's different, why the user needs it and what the user must do to get it; the so-called "call to action".
However, liking the thing you're writing about is not required in order to be a UX writer—if it were, there wouldn't be any UX writers.
Nobody "likes" writing copy for validation errors.
So don't be discouraged if you're not a sports fan but you've got to write a registration screen for a football app. Take the user's perspective, evaluate the features of the application you have to work with and envision what would get someone excited enough to want to sign-up.
As you're writing, keep asking yourself "what is the most compelling feature of this product? What would motivate a target-market user to take action? Does this copy bring both to the forefront?"
If you've got a market research team at your fingertips to answer these questions, then you're in luck.
If you've just got yourself and your uncle Larry (who is a massive Colts fan) then run your copy by him. All user feedback is "good" feedback in its own right, but an opinion is especially valuable if it's coming from a target-market user.