One of the problems with creating longer-running fusion reactions is that if they do it, in order for the reactor to not wildly overheat almost instantly, they

One of the problems with creating longer-running fusion reactions is that if they do it, in order for the reactor to not wildly overheat almost instantly, they need a massive cooling system to carry the generated heat away. At that point, you almost might as well hook up a steam turbine loop and generator and put the power on the grid. There's lots of other problems too - I don't think they have a well-tested solution for adding fresh fuel and disposing of the fused products on an ongoing basis.