When pushed further to answer why, surely her answer was simply "Because heat pumps are rubbish".
Our clapped-out ancient 1970's hot water tank system boiler finally gave up last year and it's the first time I've been glad that our landlord is a massive cheapskate - because the rental agency priced up both a "state of the art" heat pump and economical low-energy-use hot water tank system, with the other option being a cheap 'n' cheerful new gas multipoint boiler.
They went with the cheaper option and we got the gas multipoint.
Unlimited hot water!! Yasss.
It feels like it was a blip in history. We used to have oldschool water tanks where the water ran out... then we had a few glorious decades of instant hot water... and now we've gone back to "new age" water tanks
.