So, one USDC is always equal to one US dollar ($).
But when you buy cryptocurrency with regular money, you see that the amount in USDC is less.
Why is that?
Each payment service charges a transaction fee; the amount of commissions is different.
Most often, the commission varies depending on the amount of the purchased cryptocurrency.
The rule applies: the more you buy, the more profitable it is, because the commission is less in percentage terms.
For example: if you buy 50 USDC, then the average commission will be about 8 US dollars ($) (15% of the amount); but when you buy 200 USDC, the average commission will be about 20 US dollars ($) - 10% of the amount; which is much more profitable in percentage terms.