Why? Couldn't you just take the whole payment via bank transfer and then go buy Bitcoin afterwards if you wanted to? This sounds like extra steps that I don't understand the point of.
Many of us have more bitcoin or other crypto than dollars at any point in time, directly onchain (as opposed to on an exchange, which can have extra steps or even the same limitations as any other financial institution). Even if we have a whole portfolio of other assets, its still not dollars available for trade.
If we want something instantly, internationally or outside of business hours or at a large amount, the bitcoin can accomplish that pretty instantly (few seconds with lightning, 1-20 minutes with 1 confirmation onchain transaction). Almost every other crypto asset can do it even faster.
Some people will never get it