There's lots of demand when the payback is very quick and easy. Batteries being built right now make tons of money on grid stabilization services. But once those easy gains have been taken, making the less certain investment scaling up the batteries to handle that cold snap that happens a few days a year etc will not happen in the free market.
In a free market, where everyone is free to ignore consequences, coal would be the obvious solution - but if the climate change costs are priced in - then batteries do become attractive.
Lightweight ultrapower batteries are high tech. A simple batterie for the grid, that can be big, is not and quite simple to build.
We started to price in the CO2 externalities - and demand is skyrocketing.
Subsidies are more of a geopolitical/welfare thing in this context.
> Why not? There is a worldwide and increasing demand for them.
That demand is created by the variations in prices created by renewables, which are themselves subsidized. In a world with coal, gas, nuclear or hydro, there simply is not enough demand to develop batteries.
So, in a world with no subsidies, how do you pay for batteries, not good ones but bad ones for decades until the industry ramps up? It simply doesn't happen.
It's not an indictment either. Subsidies are simply the way heavy industrial investments work, and in the electricity sector investments are so massive that without subsidy, barely anything happens.