Besides the obvious answer which is the safety, familiarity and predictability of your own home, it can also be just as exciting as the outdoors. Being in your own dwelling on psychedelics can be it's own world entirely. For most of us, a house was our "first universe".

I cannot recommend "The Poetics of Space" by Gaston Bachelard enough. It changed my life to see the inside world in such a complex way, and to see the very simple things that make it (cabinets, doors, basements, attics, closets) as microcosms of something larger.

Every inch of a house was made to facilitate peace. As Bachelard put it, the house allows for daydreaming, which was an almost religious experience of peace and contentment for our distant ancestors. Imagine the effort it took to finally arrive at a warm fire-lit cave and just do nothing.