Intensity.

I just googled 'demolish habitats' and got 174 hits. I then googled 'destroy habitats' and got over 18,000,000. 'Demolish' is just about possible, but it isn't a very natural collocation. 'Demolish' suggests systematic dismantling, such as when a building is deliberately demolished. In most situations where habitats are destroyed, this is an accidental result of another practice, such as deforestation for road-building. 'Destroy' is much more appropriate, and is a natural collocation.

Demolish usually refers to a building or monument. (Knock down) Destroy can refer to anything else, e.g.. feelings, objects, paintings