So do the roots of trees and shrubs gradually working their way into crevices. The lava rock will break down eventually on its own. The point is whether the National Park Service should permit humans to accelerate the process. Not only the rocks themselves, but also the plants growing on them, are subject to destruction. There is little soil and limited plant growth on the lava flows.
Nothing grows on the surface of the rock except lichens.
Lichens hundreds of years old may be only inches wide. If destroyed, it may take decades for them to reestablish themselves. Trampling may also kill wildflowers and other plants. The National Park Service strives to keep as much of Craters of the Moon open to the public as possible. However, sometimes the level of human impact is too great, and protective action becomes necessary.