If my role is primarily maintaining a large complex legacy application where you're solving scaling issues, there might not be a measurable outcome to report like delivered that feature etc. How am I supposed to give my updates without freaking out that I will be seen to have done nothing (ie solved the problem).
Secondly, if doing R&D, how do you update that you did a thing when it's not anything of note.
Richard Feynman was one of the best physicists from the 20th century. He helped creating the atomic bomb, and he worked on quantum electrodynamics. He received the Nobel prize in Physics in 1965 for his work on quantum electrodynamics.
When he worked at Cornell he suffered from a (small) burn out. He did his teaching duties, but, for his standards, produced very little more than that. He was worried that others would be disappointing in him, as it was impossible for him to live up to the expectations of others. This is were he developed an interesting idea: "You have no responsibility to live up to what other people think you ought to accomplish. You have no responsibility to be like they expect you to be. It's their mistake, not your failing." [2]
If this task doesn't have measurable outcomes, or if you have nothing to report, than so be it. You tell that you have nothing to report. The company hired you to do this task, and they took a risk by putting you on this task. If you have nothing to report, than it's their responsibility to do something with that. Not yours. If they want to know why you have nothing to report, they will probably ask you to explain why you have nothing to report.
Footnotes:
[1] - Actually, I recommend reading the whole book. It's very funny and interesting at the same time.
[2] - Page 199, changed "I" into "You".