Because the whole field is an easy to debunk bullshit which is worthless in practice. If today somebody came up with a working thermonuclear reactor with a posi

Because the whole field is an easy to debunk bullshit which is worthless in practice. If today somebody came up with a working thermonuclear reactor with a positive energy output, nothing at all will change in energy markets, because it basically means you are getting a complex and expensive steam boiler that runs on effectively free fuel. But even electricity made from coal has only 20% of the coal price in it, meaning, there won't be a dramatic improvement in energy cost if fossil fuels were free. Renewable energy today provides very cheap energy inputs and no improvement in this field can yield any dramatic difference. And everything that comes further downstream has to be paid, anyway. Research in it is still a good thing though because a lot of other discoveries and technology improvements are done on the way, bringing benefit even if result itself is useless (like with the moon landing).