Why isn’t virtual currency allowed in China?

Illegal cryptocurrencies have already, to some extent, perfectly circumvented foreign exchange controls. If cryptocurrencies were legalized, it could even render the Golden Tax Phase IV system obsolete.
For example, if you sell an apartment in a first-tier city and receive 5 million RMB in cash, and you want to exchange that for 700,000 USD to transfer abroad:
The bank’s foreign exchange purchase limit is $50,000, and the remittance limit is also $50,000—a double safeguard—so it would take 14 years to complete the transfer.
If you use someone else’s quota to exchange for US dollars in cash and carry it out yourself, any amount over $5,000 per person is subject to regulation.
If you use someone else’s quota to wire funds to your overseas account, using more than three people will draw attention. If you want to take RMB out of the country and then exchange it for foreign currency, the personal carrying limit is 20,000 RMB per trip.
If you want to wire RMB abroad, sorry, you can’t send out even a penny. All the legal paths you can think of are completely blocked. Now, back to cryptocurrency—
If there are no quota restrictions, you can circumvent everything perfectly. Even if there are quota restrictions, say using the foreign currency $50,000 benchmark, you can use the quotas of 14 people to help you exchange 5 million RMB, then store it on a USB drive and take it abroad. As long as you don’t tell anyone, nobody would know.
Summary: In a sense, cryptocurrency is a general equivalent similar to precious metals; it has properties like precious metals: decentralization and anonymous transactions. This means, for a centralized national treasury, it is completely out of control.
As times progress, precious metals have gradually withdrawn from circulation, mainly due to the constraints of physical laws—they are far less convenient than fiat currency. But cryptocurrency isn’t restricted by physical laws, and is almost as convenient as payment platforms like Alipay and PayPal.
Even putting aside the issue of foreign exchange controls, if everyone were really allowed to use cryptocurrency, Golden Tax Phase IV would become a joke. Who could tolerate that?