Funny thing is that many people don't really think about the theme of their work, which is why they're having trouble describing them in a concise manner.
Trying to come up with a one sentence description about your game can really help you nail down what exactly it is, that makes your thing interesting, which in turn can help your creative process. It's also a nice opportunity to try to come up with unique descriptions that don't rely on you comparing your work to someone elses'.
Also the Elevator pitch (at least as far as I understand it) is meant as a gateway to convince people to listen to your more in-depth explanation. Sure, it's shallow but most conversations with strangers start on a very shallow level. Also just because you can describe a thing on a superficial level, doesn't mean that the thing itself has to be superficial. It's all a matter of perspective.