It's there in Civic X for lower ride height. Previously the ride height was more. But rear exhausts have to cross the undercarriage and need space. Eliminating the hump would have made them hanging under the floor resulting in pipes getting damaged with every bump or speed breaker.
That's the logic I think has been applied. Please correct me if I'm wrong.
That's the part for floor hump, about the seat hump. It makes passenger side more bucketish and there might be something underneath that area too, like I guess the fuel tank, filter and its connectivity was underneath the middle seat on an 8th Gen.