Funding at the level in that chart would not have given us fusion. That chart is based on a crash program to develop tokamaks, but assumed tokamaks work better than they actually do. The main product of that crash program would have been tears and frustration, not practical fusion.

One can turn this around and say that fusion not getting the funding in that chart is evidence it was not seen as a promising place to invest. One cannot simply presume it's a good investment and ignore any evidence to the contrary.