Binance want more and more money, as usual. And they want to push you to use BUSD
If they want to push using BUSD it's not matter at all since there is benefit on using their stablecoin instead of tether and usdc. I know this cause I'm taking advantage of the busd. Holding it, can give you free token reward from launchpool and no fee on trading busd pair tokens. If you used usdt on trading the fee is huge unlike using busd which is totally free.
And, we are not forced to do it unless if we like it to do so. Binance wanted to promote their BSC and that is clearly their strategy but worried if that only be the reason that people will look for another exchange.
Binance is on the lead now among other exchanges and that brings them confidence with their decisions and they know that the trust from their users will stick to them no matter if the fees will increase.