Pretty much any and every energy system needs lots of storage - either real, or virtual in the form of demand-side response.
The old energy system, the one we inherited, had absolutely vast amounts of energy storage built into it, in the form of oil, coal and gas storage. And that's the main reason there's no market for STES.
But for about 40 years, we've known that the price for that was way too high - the pollution is destroying us.
However, it meant that for a very long time, there was no economic incentive to build much storage at all. The only storage that got built, really, was either to cope with inflexible nuclear power (overnight storage heaters) or their intermittency (pumped hydro storage to provide rapid-response power within seconds, for a few hours, when very large power plants drop off the grid).
And because most countries have had powerful incumbent fossil fuel supply chains, then although this is a problem we should have started fixing 40 years ago, many countries are only starting on it now.
So, we have little understanding of how to build seasonal thermal energy storage (even though it can be pretty simple engineering), and of its whole-life costs. And there's still no market for it.
Some places, such as Denmark, are building larger stores for their district heating schemes. And to their credit, they did start on heat storage decades ago, in response to the 1970s oil crisis, and never stopped.
Other places are now looking at thermal energy storage of various forms, and there are demonstration projects in place.