My wife showed me once a chart of both founding and the estimation of the fusion spark (plus net energy). It explained pretty good why the estimation had changed.

My impression is that if humanity had focused on the question and not the politics we would already have fusion capacity.

But do not forget, we still do not know if it is financial benefit to use fusion in the future.

For the last 60 years even! Fusion power was ~20 years away in Stanislaw Lems Summa Technologicae in 1961.

This is mostly because it has not been funded to the level required for that timeline to be accurate.

https://upload.wikimedia.org/wikipedia/commons/a/ab/U.S._his...

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.