"If 2000mA = 2A why do they confuse things by using 2000mA?"
There is no confusion: 2000 mA is unambiguous.
But in engineering, 2000 mA equals 2.000 A, not 2 A.
So a PSU manufacturer would be stating that their PSU can supply up to 2.000 A but not 2.001 A and above.
I doubt here that the PSU manufacturer is using a circuit that goes into current limit that precisely, down to the milliamp.
It's more likely that they express it in mA because that unit format allows for an existing/possible range of products that do go down to lower max. mA. For example, if they want their spec format to support a 100 mA PSU, a 250 mA, a 5 A and so on.
Look on the websites of the larger PSU manufacturers, at the products in a range. You'll see that's why the same units are used to make a range of products easier to differentiate between.
It's not some marketing attempt at making it look more impressive or anything like that.