To expand on it a bit. I am sure most of that is just business inertia. They've been hand sculpting metal for so long it's just easier to keep doing that. They have repatedly stated they aren't switching to plastics since it would take too large and investment for their company.
As far as 3D printing goes, they have looked into it and are currently doing a sort of pathfinder project with the Land Air Mechs to test the feasibility of having the masters modeled in CAD and printed.
Back when the Star League LAMs were fan funded, they originally suggested they wanted to try doing that, but their lack of solid information led to them lowballing the figure massively thinking they could do it on the funds it would take for hand sculpting, but then found out they couldn't. Several months ago they took another crack at it by doing a kickstarter to fund the WoB LAMs for the same process in collaboration with a 3d printing company near them. They overestimated the cost that time, so that when they added stretch goals they put the first item at $100 over the funding goal, and even after missing the last stretch goals they seem to be committed to bringing us all the LAMs.
They went with the LAMs because the artwork was done as 3d models by Stephen Huda, who made the models available to IWM, so the sculpting cost was already sunk by Catalyst Games Labs and readily available making it the perfect choice. The whole thing seems to be a learning experience as I have heard through their postings they have had to make some adjustments to the models a bit to mold right, and the company doing the printing itself needs a bit more experience with the requirements for miniatures since that's not the sort of thing THEY do.
Hopefully things work out and IWM manages to make it feasible to make more of their minis this way; even with their crappy phone camera photos from gencon, you can tell the detail is pretty good, hopefully it translates to the metal.