Can somebody explain please why potential off-take partners need...

Can somebody explain please why potential off-take partners need a "demonstration plant" to make their decision? I understand they need to see drill-results to understand the size of the resource. I understand they need samples to check the quality of the product. But shouldn't that then be enough to make a decision? I can imagine that the process to extract cobalt on a large scale is not easy to build, but it has been done elsewhere so it's not an invention in itself. My overall impression is that investors/off-take partners are for whatever reason not making a decision, so COB is always aiming at the next "big milestone" which is then hoped to change everything. Would be great if you guys can share your views. What is missing for investors/partner to make a decision? Thanks