If houses got cheaper every year, very few people would want to buy them, and people stuck with mortgages would have a powerful incentive to walk away from them. If cars got cheaper every year, then people would put off buying new cars for longer. If gold got cheaper every year, then a lot of gold coins would be dumped on the market.

If everything got cheaper every year, then people with money in the bank (or under the mattress) have an incentive to reduce how much money they spend, in general. This would lead to factories reducing their production and laying off employees, giving the remaining employees an even more powerful incentive to hang onto their savings.