And this is indeed a good thing.

Capital that was malinvested during the boom period has to be accumulated again to return to previous productivity levels. The method to accumulate capital is saving.

That graph doesn't show that people are hoarding cash, it shows that they are saving. If they're investing in stocks the money doesn't go out of circulation and if they put it in a bank it mostly doesn't go out of circulation. All of which isn't to say that there are people or institutions hoarding money, only that your graph is irrelevant to that.