Bitcoin's automatically adjusting difficulty rate means that if fewer people are mining, then it becomes more profitable for them, which guides the system into an equilibrium.
Also, mining profitably requires special hardware built specifically for Bitcoin mining.
> Also, mining profitably requires special hardware built specifically for Bitcoin mining.
For bitcoin yes, but there are proof of work cryptocurrency systems out there that use CPU. And there are proof of stake systems out there that neither cpu or gpu intensive.
For a lot of people, cryptocurrency = bitcoin. But there's a growing number of crypto enthusiasts who see crypto as an constellation of cryptocurrencies, each with their own unique attributes and fundamentals, that complement (as well as compete with) bitcoin.
Also, mining profitably requires special hardware built specifically for Bitcoin mining.