I'm asking if there is any information on why they chose to make kilobyte = 1000,
Because kilo means 1000. It simply doesn't stand for 1024. The same way 13 inches aren't a foot.
So I'm interested in the arguments used and the decision making process that lead the IEC to decide that kilobytes would be redefined as 1000 bytes,
There was no redefinition, as 'kilobytes' isn't a unit of its own. It's 'kilo' as prefix with the fixed definition of 1000 and 'byte' as, well, a byte. So kilobyte always meant 1000 bytes.
These prefixes are part of the International System of Units (SI) — though, they had already been used before, since introduced with the metric system in 1795. Within SI there are no different units for the same thing (like inch, feet, yard, furlongs, chains and miles for length) but always only one (meter for length, ampere for current, and so on). To use them in different circumstances they are prefixed according to powers of 10. A very convenient system.
And it was sloppy engineers who used this convenience to describe certain binary values with somewhat close values — as 2^10 is 1024 and thus close to 1000. These were never official units in any way, just a kludge to get along. Standard documents always used power of 10 pefixes — which leads, by the way, to the effect of serial transmissions always being decimal - a 9.6 kbit line transfers 9600 bits per second, not 9830 :)
When computers came out of the closet in the 1980s, people stated to recognize that these 'kilobytes' aren't really a kilo of bytes but different, so it was common to capitalize the K, as the SI prefix uses a lower case k. Nice idea - as long as memories stayed in the range of a few dozen to a few hundred KB - but when 1024 KB were reached, it broke, as the SI prefix M is already uppercase.
In the late 1980s/early 1990s it became obvious that there is a need for a clear meaning, so an international standard was proposed - and accepted in the late 1990s.
It's now more than 20 years later ... heck, not even the English complained that long about the loss of their non-decimal currency.
and the creation of the rather awkward "kibibytes".
The binary prefixes are anything but awkward. They offer an easy, convenient and well-defined way to operate with (almost) the same prefixes as for any other unit, but now making it binary, which does make a lot of sense for computing, doesn't it?
It may be useful to add a bit of common sense before going into rather pointless nagging about how it sounds or how much we're used to the imprecise way it always has been. The main point about these binary prefixes is in writing, not speaking. When talking there is context. Continuing to say 'kilobytes' when KiB are meant should be fine. After all it's much like asking for a pound of meat in a metric country works, though hey will give you 500g :))
Just write the prefix always uppercase and add a lowercase 'i' for binary and there's no more confusion.