Bitcoin has been going through the same way until today, sometimes bubble then decline
when everyone with the desire and means to buy in and has already bought in, there's nobody left to buy in at a higher price
At that point, bitcoin price will significant decrease again due to many adopters don't want miss out the chance to get profits, sell at higher rate.
bubbles that will soon pop as price crashes back to near-zero.
But not to near zero obviously, just a bit dip for a while because it always increase over time.
That isn't just a theory as we have seen the prove over the past 8 years. People believe in bitcoin and support its existence on economics circulation.