This particular sentence has not been flagged a lot.
When we do see a sentence that has been flagged a lot, that's exactly what we do -- we try to think of all the possible options. However, we are volunteers rather than robots, and therefore do not come up with all at once. The point with having a beta stage of a course is to crowdsource this wisdom from the users, which is why it's important that users report missing translations. (They do report a lot of incorrect suggestions as well, which of course takes quite some effort to wade through.)
When I wrote the above comment 4 months ago, I wasn't on the contributor team yet. Now when I can see all the sentences in the course, I'm not sure I agree with my initial opinion. That's because the course also teaches "voi ei", which is a closer match with "oh no". I'll have to check what the rest of the team thinks, when I have the time. But as mentioned. this sentence is not a high priority compared to many others, and when it's changed that change should be made also for other sentences using the same expression. Otherwise we'll have user complaining about lack of consistency...
So if you feel a certain sentence needs a fix -- report it. That's what counts (objectively)!
Finally, what user should always keep in mind is that this is a Finnish course. Therefore any problems, missing options, or inconsistencies with the Finnish will always get higher priority for me than that someone's preferred English translation wasn't added yet.
Please see my message above.
Regarding frustration, it is pretty pointless to express it here in the sentence discussion, where we might or might not stumble across it. The only reason I'm seeing these latest messages is because I replied to this thread before.
The way to actually make a change is to report missing translations the way I described. Those reports inform us on which sentences objectively need the most attention, not just which users feel the need to vent.