I had a chat with Vlad Belonozhko regarding this topic today as it was quite heavily discussed on the forums.
The main reason from what I was told is that they recently had some issues with people claiming their IEMs were actually stolen and remolded, and asking for replacements, compensation etc.
He and I also agreed that purchasing a CIEM to then resell it is quite odd in of itself, as you can really get a third of its value back at best.
From a business point of view (my words not his), it is the same effort for 64 to remold and IEM as it is to build a new one from scratch. There isn't a single part of the process that gets simplified by the fact that it is a second use IEM. The difference is, that at the same cost of labor, one gets them 600 dollars, the other does 3000 (case of 18 for example). If I were in their position I would also not offer remolds.
If you want to resell an IEM, why not just stick to universals?