[Symmetry]

It's not that it's difficult, its just that it's not perfectly efficient. So once you include the inefficiencies of the heat engine it not necessarily producing energy on net.

But there are also some engineering challenges to work out in employing heat generated like this to drive a heat engine, at least with somethings decent like 30% efficiency.

[greggarious]

Is ~30% what other sources achieve?

[Symmetry]

Other sources can do better but the problem of transferring heat from plasma erupting in a vacuum chamber lined with mirrors seems really hard to me compared to the problem you have in a natural gas power plant, say, so I'd expect even a well developed laser pulse fusion power plant to have a lower efficiency.