There are many possible reasons. You might enjoy the feeling of independence or self reliance that supplying your own power brings. You might be a weed grower and not want to be found out because of your energy bills. You may feel that it's more responsible to produce your own electricity and have a clear understanding of its environmental costs. Grid power may be unreliable in your area, or expensive. Maybe you think that power lines give you cancer. Maybe grid power is simply unavailable in your location.
HN user
oloboWd
Water and sewage -- Most people in rural america and even in semi-suburban america already use their own wells and septic systems for water and sewage. Likewise with trash, many people drop their trash off at the dump/recycling center themselves. Broadband, yep, no DIY solution there but various forms of wireless internet are available that make it quite feasible to have a completely unwired home if not disconnected.
One experience like this would be enough to put me off of home automation for about 10 years. I think its unfortunate that Nest chose a target so fraught with safety implications for their second device. A lot could be done to ameliorate problems like this if the consequences of a false negative were not so catastrophic.