[mythhabit]

Because everything (except SSDs now a days) in a computer, on a fundamental level is either 0 or 1. So when you want something that maps to that, 2 to the power of 10 is exactly 1024 bits. Somewhere along the line, someone decided that accuracy of that mapping was more important than adherence to the exact meaning of kilo.

The alternative, would have been to use something else than kilo, mega ect., that represented the base 2 magnitudes. It would be awkward to say you have 8.306.688 bytes of ram if you need to be exact.

[teaearlgraycold]

We have that alternative. KiB, MiB, etc.

[mythhabit]

We have that now. We did not for the formative years of the field.