The underlying claim to this statement is: more storage could easily be built because it is economically feasible.
Which is - apparently - not the case.
Apparently, the end consumers of electricity (private households, businesses) are not willing to pay enough money for more storage. Or the other way round: storage is too expensive for it to be deployed at a significantly greater scale than it currently is.
Cheap electricity storage is a tough problem. If storage was much cheaper, we'd see much more of it being deployed.
As always, politics has all the levers to set the direction here. Subsidize storage massively and more storage is what you'll get.
What politics can not do through such policies: lower the overall cost of storage for the consumers of electricity (apart from stimulating effects such as economies of scale, ..). Why? Because the subsidies will still be paid by the consumers in their role as tax payers.
You don't get around the fundamental principle that everyone is sensitive to prices. If electricity storage were cheaper, we'd have more of it.