Thread title says it basically.
The price of bitcoin is the last price someone paid and someone sold for it. Nothing more, nothing less.
When someone who got in early sells and makes $300, someone who got in later loses $300. It is a zero sum game. For everyone who makes money, someone loses money. This isn't stock where there is a business behind it with profits, losses and reinvestment and where people are employed. This isn't a bond (loan) that generates interest.
And it isn't a dollar. A dollar is what things are priced in. It is not a speculative asset. You can't compare the "value of the dollar" against an asset value because the dollar is what things are priced in. Nobody holds dollars. They hold stocks, bonds, real estate, etc. And most people are short dollars, they have borrowed dollars and bought assets (mortgaged homes, financed cars, etc.).
Additionally, money is taken out by miners in terms of coins mined and transaction fees. Every time an exchange is made, money goes to the miners. If the transaction fee was 1%, after 10 transactions, the miners own 10.46% of the bitcoins transacted.
There is no money "in bitcoin". Bitcoins are exchanged for a price. If there are no buyers at the current price, you can't sell. You can only sell to another buyer. And there is nothing behind it. Saying "there is nothing behind the dollar" and trying to compare it to the dollar doesn't make sense. Things are priced in dollars. People don't buy dollars and hold them hoping for a gain. They buy homes, stock, bonds, real estate, clothes, food. They get a paycheck each week and either pay down borrowed dollars, buy assets with it, put it in an interest bearing account (which is a loan to a bank, it is not dollars), buy stock, etc.
So, where is the money going.. money is being taken by miners and early buyers and money is being lost by people who bought in recently.