There is a logical explanation for this.
First, the volatility inherent in digital assets. The fact is that the main goal of every bank is to make a profit. The slightest fluctuation in the cryptocurrency market increases the risk of reducing all projected profits to zero. Today, cryptocurrency is showing a certain stability, but even despite these indicators, most financial institutions still prefer to provide traditional banking services for corporate clients, whose activities they understand.
Secondly, banks are reluctant to accept cryptocurrency due to the current rules for the circulation of electronic money. By the way, these rules will be tightened even more. For example, Russia plans to pass the draft law “On digital financial assets” (DFA). But this project contains a number of contradictions. It recognizes digital currency as a means of payment, however, prohibits the use of it to pay for services or goods. This inconsistency will result in financial institutions simply not being able to process cryptocurrency transactions.
Third, cryptocurrency has a particular impact on the economy. Many countries simply do not want their citizens to use cryptocurrency in their calculations, business or investments. The economy of each country is determined by the purchase and sale of currency, and operations related to cryptocurrency can seriously affect its development. And until countries fully decide how their economies can profit from such operations, the rules for the circulation of digital currencies will only get tougher.
Decentralized Cryptocurrency is not controlled or limited by anyone alone, there is no single administrator and regulator. Not a single financial, tax, government organization can influence the actions of participants in the payment system.
Ethereum is a multifunctional virtual platform on which blockchain-based applications (online services) are created. Applications work as "smart contracts (smart contracts)" that exclude third parties (intermediaries) in the transaction process. On their basis, it is possible to create a platform that will stimulate banks to lend against the security of cryptocurrency without fear of losses, and this, in turn, will interest the financial sector to place its assets in cryptocurrency?

In solving this problem, I took as an example the existing US financial system.
Assuming that Ethereum is the Dollar, and the smart contract is the Office of the Comptroller of the Currency of the United States (OCC), and ETH-WORLD tokens are the Securities of the US Treasury, we get a financial model of a new decentralized economic system based on cryptocurrency. I implemented all this in my project, in contrast to the existing Fiat, it completely lacks an external emission regulator and is managed by the smart contract program.
http://prosh.info/smartcontract.html