There just are not enough sellers left to push the market down in any meaningful way.
The whales always have the bitcoin and money to pump & dump the market. The price cannot always go up as there is a lot of manipulation in the market.
Also consider that people also earn money when the price is dumping by shorting through future trading.
That was the old whales that wanted to see bitcoin go up and down and make profit from that, these days we have public companies that buy bitcoin in billions, which means they can't just buy and sell to manipulate the market because we would know about it and know what they are doing, looking at what they are doing so far we can see that they have been buying and holding, tens of billions of dollars worth bitcoin was bought and hold during the last 1 year, and that is going to be the case for a long time as long as public companies keep buying bitcoin.
This doesn't mean that there is nobody that does the old method where whales dumped and pumped to make money, but it also means that there are competition now that buys and gets it from them, corporations are collecting as much bitcoin as they possibly can to have more bitcoins these days.