By "wrong reasons" i am referring to the intentions of those new users.

Say your users are predominantly seeking long-term relationships, and your branding supports that. Then a bunch of men, fueled by gender-ratio marketing, flood your app seeking hookups. You will see short-term a bump in engagement and payments. A/B testing will suggest everything is great. But long-term your product loses value as your users lose faith in your ability to deliver on what they signed up for. The (in this case women) leave and the product becomes another graveyard.