> 1. Make them huge

That more or less puts it out of reach for homeowners, condo dwellers, etc. You need a big expensive coordinated project to get that built.

Meanwhile, as an analogy, solar panels are within reach for a homeowner. Seasonal thermal storage will need to be more modular / modest sized for it to be widely applied. The potential for storing heat by forcing endothermic reactions (where you later extract it by running the reaction in reverse) has a lot more potential to be "homeowner sized".