Smiley noted, and yes DL's IT notoriously sucks, but OTOH there's no particular advantage to them to allow more granular increments. By forcing you to do it in discrete chunks, unless you are good at MQD "golf" most people will convert more MQMs to MQDs than they needed to (i.e. less RDM liability for DL), or not enough (and then fly to make up the difference). As opposed to, since you can do it on Dec 31st, if you could convert exactly the number you needed (at the other extreme), then there would be no breakage.