It's still used in some projects. I remember seeing a deep dive into a net zero lodge (for vacationing) someone built just a few years ago that featured all of those: solar water preheating & PV on the roof, as well as heat pump HVAC/water heaters. Perhaps now it would be cheaper to just beef up the PV and active water heating but I'm sure they had their reasons at the time, at least.
It's not that retro. In some places in the world it's still very common, and heat pumps very uncommon. It's a response that makes sense in the right climate (and I should note Carter did create a tax credit program for it, though it never got popular in the US).
Yes, at this point. At the time, they were not.
Seriously everyone critiquing 40 year old projects like they just had PVs laying around in the 70s.
And people incorrectly saying Reagan had PV panels pulled down, the troglodyte. /s That solar thermal collectors never really caught on in the US shows the technology was marginal and the decision to remove them (I think when they leaked?) was arguably a good one.