I'm aware of the arguments about how it can be that much cheaper when deployed at mass centralized scale rather than decentralized across a bunch of rooftops, however the way the electric markets are prices is based primarily on the cost to produce the marginal supply, which is usually gas.
So while the power company might flood a bunch of solar panels trying to capture the profit between cost to generate solar vs. cost to generate using gas, those profits haven't been lowering electric costs at residential rates. If anything those costs are still climbing.
It's actually not hard to get rooftop solar to pencil out in that situation, especially if you assume even moderate growth in future electricity rates or inflation. In my own tracker it would even be superior to paying down additional principle on my home mortgage!
Admittedly it would be less of a slam dunk if the net metering was less generous around here as you'd basically be required to add battery to the mix if you weren't already. But even that just prolongs the time to payoff, it still ends up having good ROI economically speaking.
Electricity generation in the event of a power outage was another consideration for me.
But yeah as a techy I also just enjoy having them.
You can't just blindly say "PVs save you money". It matters very much how much sunlight you get, the orientation of your roof, how much electricity costs, how much labor and installation costs, etc.
My location is far from ideal for solar. But with incentives - which are funded in my country via a per-kWh surcharge on everyone's electricity bills - it just barely makes financial sense to have solar panels on my roof.
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.
Off the top of my head the only thing that's really doable without replacing a depreciating asset are certain kinds of insulation upgrades. (And I guess potentially ceiling fan installs.)