Because the ultimate goal is a power plant, not just a paper saying that Q-Plasma of 1 (or 10) has been reached.

I can imagine it would be reasonable for fusion scientists to not spend effort on the Heat -> electricity part. What I think the article is highlighting is that they are currently totally ignoring all the energy that goes into anything other than plasma, (ie the power to run magnets, vacuum pumps, or lasers), which from the examples given is on the order of 10s-100s of times the power delivered to the plasma.

This energy should be considered by fusion scientists, because it may end up invalidating certain topologies that can achieve a Qplasma > 1, but can't achieve a Qtotal > 1. For instance from the article, it seems like pulsed lasers are relatively inefficient at turning input energy into laser energy, which might mean they would need a QPlasma > 100 before QTotal aproaches 1. I don't know which of those inefficiencies are deemed to be fundamental and which are potentially improveable, but it could suggest the whole line of research is not worth perusing.

Things like the NIF also have power losses in feeding the ignition. The NIF lasers are maybe .1% efficient, or less, meaning that even if energy delivered by the lasers is less than created by the reaction, it must deliver a 1000x power output just for lasers to be break-even.

Because Qplasma >> 1 might mean there's enough energy to make Qtotal > 1 as well.

They can bother with whatever they want. But stop misleading the public and the media.

What's the significance of reaching the Qplasma = 1 milestone?

They get to uncork some champagne, but they still need to get Q up to ~10 before handing it off to the powerplant engineers.