Not sure if this is a bug from an oversight or a deliberate choice, but it seems likelier to be the former. This is on Krastorio 2 1.0.3 and Factorio 1.0.

In vanilla Factorio, blue belts, splitters, and underground belts all require lubricant, so they are not hand-craftable. However, in K2, only blue regular belts require lubricant, yet splitters and underground belts are still not hand-craftable, even if I'm carrying all of the components of the recipe. Blue LOADERS are hand-craftable, and all types of green belts can be crafted by hand, even though they all require blue versions of the item. So I'm wondering if you forgot to flip off the "not hand-craftable" flag for blue splitters/underground belts since they are vanilla items. Fixing this would save me a lot of work for when I need a single blue (or higher) splitter and don't have one on hand. :)

We decide to leave it craftable because at "high level design/realism/philosophy", the loader is a composed machinery, u already craft with an assembler what u can't craft with ur hands. Anyway this will never changed, the mod is completed, we will only change exploit and bugs.