What do peopel mean when they talk about happiness?
I believe people think about this elusive eternal feeling of endless happiness.
Another approach is the story thing (concept rather than the feeling)  like knowing that at the end of life one will be able to say "this was a happy person" like that of Solon and many others (Solon told the king that he cannot be declared happy until his end, which is nonsense, if we look for momentary happiness, or even the story of every moment.)
In practice, we are fairly limited. We can improve many small things in life (so I hope). But these large gains are next to impossible.
When this fantasy takes precedence, one gives up any hope, at least practically.
Sleeping another half hour a day, does not sound an improvement for life. It sounds a small thing, a technicality. Nobosy cares if it will improve life quality. But I guess the main point is that it does not fit into the huge dream of happiness. It is not going to make you a prime minister, give you eternal bliss, or bring you ultimate love (another overstated dream).
PS. I can find rationalization for concentration on the big dreams. And life calculus are too complex to form an opinion. These are just my natural thuoghts. There are also complex topics on our subjective meanings and all kinds of psychologicval constructs. Just mentioning it to confuse you.
 story vs. feeling. Kahneman termed it "Living vs. thinking about it". (read the paper, it is provocative, althought I am informed that Kahneman has even more interesting surprises in store) We have an experience, and we have thoughts etc. Humans tend to take thoughts too seriousely. While much of life is about the espeience, not the story.