I can see this being the same issue with trying to sell damaged items on the market, which ties into why they don't stack, is that you'd need a line for each CT or broken module.
A [x] CT at 67.89% is not the same item as a [x] CT 67.88%. So the market can't just have a listing for [x] CT because they aren't the same item.
It doesn't make sense to split the efficiency from the CT, or at least not in this case, because the value of the CT is based on it. This would also mean that the entire Market would be duplicated 5-9 times for each % of CT, since you can make a CT out of 'almost' everything on the market; each module requiring a level 1 decoder can be created using all 9 levels with different %'s, so for instance it would have to look something like
CT
Miner Charges
Titan Mining Charge CT
Titan Mining Charge CT : 55%
Titan Mining Charge CT : 60%
Titan Mining Charge CT : 65%
Titan Mining Charge CT : 69%
Titan Mining Charge CT : 74%
Titan Mining Charge CT : 79%
Titan Mining Charge CT : 83%
Titan Mining Charge CT : 88%
Titan Mining Charge CT : 92%
And only slightly less entries for modules requiring level 4 or 5.
Also it's not likely that producers are going to make CT's to sell, simply because it doesn't really take any special level of skill to put the Item and a decoder into the RE, skill just saves time and a few NIC, it doesn't provide a better CT.
MK II's would be the only CT's worth putting on the market, but they can't be used again, because the way the market is layed out, it can't deal with non-standard items.
A contract system would be better, where like anything else, you can setup the ends of a trade that can be complete with one party offline.