Some people are great at coming up with viable ideas, others are more capable of executing them.

If you're the latter, it could make sense to buy a developed idea the same way it makes sense to hire a developer if you have an idea but no coding skills.

The issue, however, is that ideas morph over time (customer feedback, trial/error, etc) so be aware that if you buy an idea, you aren't buying a business in a box; Creativity is required every step of the way.