Here's a reason I think humans will embrace space habitats and colonizing other planets: we can't let go of the idea of infinite growth, and we want to preserve life and nature(and biodiversity). Those two facts are incompatible with each other if we remain only on earth.

So we'll build carbon-neutral space launch platforms. We'll figure out asteroid mining and space manufacturing. We'll grow beyond Earth because we will never, as a whole, accept death.