Storage hot water is actually quite inefficient.

On-demand heating has the advantage that there is no thermal loss due to keeping a large amount of water (plus piping) hot 24 hrs a day.

Plus water is not wasted in waiting for hot water to arrive each time a tap is switched on.

Back in the days of Coal-fired power stations, people were encouraged to use storage hot water systems which were automatically switched on at night, so the the power stations could continue running because of the large base-load power demand.

However the modern Solar/wind generated power systems are the opposite, they much prefer loads which are only on during the daytime.

Even with heat loss by tank, It's x2-x5 efficient if it uses hear pump water heater. Also storage system works great when solar generators are active.

On-demand HWS can use heat-pump technology if required. Even tiny refrigerators use a heat pump. If they aren't widely used, it's because the savings are too small to warrant it.

Regarding solar HWS: The cost of heating panels, piping, and installation, has meant that they are fast disappearing from the market. It's better to add a few extra solar electric panels and use on-demand HWS, either with battery storage or via grid connect.

I've just been down this route with a new solar electric plant. I had originally assumed that Solar HWS would be included, but after doing the calcs, have abandoned the solar heating panels and instead opted for a few more solar electric panels plus extra Lithium batteries. It means I have a lot more storage that can used for many different purposes.

Refrigerators are similar to tank system, rather than on-demand hot water system. With smaller heat pump, tank is needed because it can't heat water immediately. Refrigerators have small heat pump so that's similar thing. Both should have good insulation.

Heat pump heater can be run when solar panel generates so much energy (energy price is low). That's a similar thing as batteries for energy use time shift.

You do usually, but with a gas combi boiler. Electric showers aren't that common in the UK either (23 years here and never seen one in person; but had never heard of them before moving here...), and usually a hack when putting a shower somewhere that didn't previously have plumbing.

Electric showers are a result of low quality, cheap-as-possible housing.

I've seen them (my parents have one) in the UK, and lower income countries in South America, Asia and Africa.

Historically hot water in most houses in the UK came from a gravity fed tank in the attic. This means low pressure. If you wanted a high pressure shower, your options would be to replace the gravity fed system with a cold water pressure system (which can be expensive and might also involve disruptive relocation of pipe work) or to just fit a cold water fed power shower.