There are lots of cryptocurrency payment gateways. Each of them have different processing fees and transaction fees. some of them charge 1% to 5% fees on each transaction. which is a huge amount but merchants have to pay this amount. But there are payment gateways who charge the lowest amount like, one payment gateway only charges 0.23% processing fees on transaction. I find it very attractive because merchants will get more from it and it will be more beneficial for them eventually.
Binance charges on altcoins when selling while bitcoin selling in binance is free. But other exchange platforms charges higher. It is only on wallet transaction that different wallets charges differently, in Electrum the fees might be 2.4 or high. Nobody likes high fee payment platforms to do transaction. Binance is everywhere and their fees are okay for the average person to make buying and selling.