The thing you are missing is that in addition to fusion power research (which is valuable and NIF has made major contributions to) there is also fusion weapons research. Inertal confinement is (kinda) close to the conditions inside a fusion bomb, and NIF also has a mandate to research those conditions. For that kind of research, a single pulse of fusion ignition is exactly the kind of data they need. Since we have a nuclear weapon test ban, and computer simulations need some kind of ground truth to be calibrated against, achieving fusion ignition in a lab is valuable to NIF for that reason alone.