>Why is it so underfunded?

- Oil/coal/natural gas lobbyists and interests which hinder tax payer funded research.

- The fact that there is no guarantee we will ever figure it out and no idea whatsoever as to how much it will cost to figure it out. Investors like returns, in their lifetime, leaving largely tax payer funded research as the greatest source of funds... see above.

And then with government-funded research... if a government figures out fusion, what do you do with it? Do you license it to private industry? Do you make state-owned power plants?

If you give it to private it industry, it's going to get to other nations. If it gets to other nations, you lose non-electrical power and create potential strategic issues, which means you are motivated NOT to share the technology.

It sucks.

I wish we could all just get along, fund stuff like this and space exploration, and get over petty politics before our species goes extinct.

Because we already have a functioning fusion reactor.

Utility-scale PV now costs only $43/MWh. Investing in developing fusion reactors makes very little economic sense compared with capturing the output of the fusion reactor we already have.

The research should still be done, of course. It can have benefits to a future interstellar civilization - but until we're interstellar, PV is far, far more compelling.

Historically, Fusion has been bad at predicting when it's going to be ready for prime time, that plus very early fusion experiments turned out to be a lot of duds. Just think of the Cold Fusion hype (on a side note; cold fusion does work, µCF replaces electrons with muons in the hydrogen atom which reduces the radius of the atomic nucleus such that fusion becomes possible at room temperature and far below but generating the necessary muons is a fools game) and the various other nuclear fusion failures.

Fission on the other hand could report a lot of results and success and, at the time, seemed to be infallibly safe.

Same reason preventative medicine is not practiced. The upfront costs are great and the out come not certain leaving many hesitant to invest in something they may never benefit from. Especially if your country has more immediate pressing matters that you could fix right now with that money.

Another (completely stupid) reason is that it's "nuclear" energy. The general public has a hard time understanding that fusion and fission have very different risk profiles. I recall that after Fukushima some countries cut their budget for fusion research because nuclear energy is clearly bad and unpopular.