The mantid have statues built on Sra'vess. We don't know exactly what they use them for. They may have some sort of religious significance, or maybe they assist with their sonic communication.
When you fight your opponent, you don't just engage them physically, you also engage them mentally. Whatever they use them for, the fact is that those statues are important to them.
Which is why I want you to blow them up. Losing something important will be a substantial hit to morale.