I wish that were true, but I suspect more people are doing it to be trendy/appear "green" than basing it on a system lifetime ROI calculation vs. alternatives.
You need only have read the HN front page 4 days ago to have seen one reason why 50,000 people may be motivated to get solar. Nothing trendy going on there, just poor regional planning.
People are rarely willing to spend five figures on something just to be trendy or green.
Just looking into it for my house in the UK (read, not very sunny) and it'll pay for itself in around 6 years. Seems like a no brainer for a house I'm not planning on moving out of.
What alternatives do you have in mind that also have an ROI for the homeowner?
You should take this as a data point where your gut intuition has failed you.
It is really condescending to dismiss their choice as motivated by vanity rather than assuming that other people might have done their homework and made a rational decision. It might very well be that you have done your own homework and it doesn't make sense for your situation, but other people face different tradeoffs which make it worthwhile.