They raised the transaction to 1usdt per withdrawal over a month ago, probably because trc20 usdt was getting more deposits and withdrawal is than their BUSD, so they decided to make some money off usdt withdrawals, and it's no longer just Binance last week I tried withdrawing TRC-20 USDT from kucoin and I was charged $1 too, seems like very soon time every exchange will want that too.
Binance want more and more money, as usual. And they want to push you to use BUSD
Everyone wants money, that's just the main aim of doing business satifybthe customers then make money off them, that's just business for you.