According to the Binance article that I read about it through the twitter link that you posted above, not only USDC, but USDC, USDP and TUSD.
According to the Binance article, people will still be able to deposit and withdraw in USDC, USDP and TUSD. But for trading, it would be automatically converted to BUSD on Binance. But if you deposit USDC, USDP and TUSD, you will be able to withdraw in the respective coins.
It is another strategy of Binance to shill their BUSD and enforce their users to use BUSD more.
Months ago, in 2020 when Ethereum network has very high transaction fee up to $200 per transaction or higher, people switched to use Tether USD on TRC20. Back in those days, Binance provided 0 transaction fee for USDT TRC20. Months later, when they started to shill BUSD, they stop free withdrawal fee for USDT TRC20 and if users want to have 0 transaction fee, please use BUSD.
This time, Binance again applies this strategy and I am sure they will get another success. When you are on home of others, you can not ask for completely fairness and fair competition.
I can see other exchanges doing this. Allow deposit and withdraw of any of the big name stablecoins but only trade on 1.
Do you really need BTC/USDC and BTC/USDT and BTC /BUSD? And then every other altcoin/ 3 stablecoins?
All come in -> converted to one -> choose your outcoin.
DaveF has a point too. Personally it is unnecessary to have multiple trading pairs for one coin. I think only two trading pairs are enough, one with Bitcoin and another with one stable coin. Assume you trade BTC to BUSD, but don't want to store your money in BUSD, you can convert your BUSD to your favorite stable coin. It costs you a bit more trading fee or conversion fee. It gives more income to exchanges and reduce their maintenance, security costs.