> why we [we]ren't we able to harness the computational model to identify it theoretically and develop a method to produce it practically prior to this.
Because the computational requirements are off the scale in the most literal sense. The search space is so large that you won't be able to come up with an improvement in efficiency for your search unless you guide it very carefully with experimentally obtained results and that's exactly what these people were doing as far as I understand it. You mix up a batch of stuff, test it for gross properties, do crystallography and then use the information from that to do some numerical simulations to check if your assumptions and observations hold up.
Because the computational requirements are off the scale in the most literal sense. The search space is so large that you won't be able to come up with an improvement in efficiency for your search unless you guide it very carefully with experimentally obtained results and that's exactly what these people were doing as far as I understand it. You mix up a batch of stuff, test it for gross properties, do crystallography and then use the information from that to do some numerical simulations to check if your assumptions and observations hold up.
I don't think we had this compound before.