If I may ask, how do you mean using bitcoin for payments is cheaper comparing t fiats? Are you being given discounts when used bitcoin for payments or what? Because I am aware that bitcoin transactions even charges for transactions fee which most little users considers as lost when executed a transaction.
It depends a lot on the type of cryptocurrency you use. Some cryptos have very low transaction fees. But even if the fees are higher, paying with crypto can still be more affordable than regular cash payments, particularly for international transfers. For instance, if you were wiring money abroad through a traditional bank you'd likely get slammed with lofty fees and exchange rates. But with crypto, you can send money directly to another persons wallet at a fraction of that cost.
Cryptocurrencies have many advantages over traditional payment methods for cross-border transactions or international payments, but will be more expensive for domestic payments. I don't even incur any fees if I pay via banking app no matter how big the amount is and the confirmation time is almost instant. While using crypto would be quite inconvenient because I have to pay extra transaction fees, how comfortable would you feel if a cup of coffee costs $1 but you have to pay an extra $1 fee if you use USDT, let alone bitcoin?
Overall, both cryptocurrencies and fiat currencies have their pros and cons, nothing is perfect.