Isn't it because if there is less demand the business will lower the price to get more people to buy their product but if demand is high the business can raise their prices so when their products are being bought they get more profit as the demand is high and the product will still be bought at any price.
Basically this, but just rewording it:
Think of this. If you're a small business, and no one/not many people want to buy your goods/services (i.e low/no demand), you still want to sell your product. But, you realise that you have to make the price extremely low to attract consumers (since there's low/no demand in the first place). Therefore, as demand goes down, price goes down.
Similarly, if there are a lot of people wanting to buy your good/service, you have the luxury to raise prices and know that people will still buy whatever you're selling since there will still be demand for it (i.e at price X, 800 people are willing to buy, but at price X + 10 there are still 300 people willing to buy - it's basically like an auction). Thus if demand goes up, price goes up.
