Very likely wine demand was not going up, and price increases were instead due to increasing costs and inflation.
So when demand softens it may be advantageous to hold back the excess rather than lower prices. Yes, there are cash flow issues when this approach gets out of hand, but financial interests can cover a lot of that as well.
Eh, not really true for the cheap end of the market. A lot of wine sold in supermarkets, for example, is meant to be consumed a couple of years after bottling, tops. And storage can be a significant problem.