There just are not enough sellers left to push the market down in any meaningful way.
There are 15 million BTC. Each of them have own value. When $30k will be to low for them price will move up. But every coin have its price. Some will sell at $40k some at $50k some at $100k. All 15 million BTC have its price. Oh and dont forget that those that will buy at $40k will then again have its own price when will sell. So these 15 million BTC never decrease.