It has been estimated that roughly only 7% of the color, "yellow", that we see emanating from everyday objects is actually Spectral Yellow (which would be represented by this "peak" to which you are referring). The other 93% of the color, Yellow, that we see is reflected Red, and Green light.
This is one reason that spectral emission curves prove to be rather meaningless, and useless for judging colors that occur in everyday situations, such as painting. For example, the color, Magenta, is represented by equal emissions (or reflectance) of both the Blue, and the Red portions of the spectrum. In fact, because those two colors occur at the opposite ends of the spectrum, there can't possibly any such "peak" in the Magenta portion of the spectrum, simply because there is no single, "Magenta wavelength" in the natural spectrum. If you doubt this fact, merely Google "Spectral Magenta", and you may be surprised to learn that there is no such thing.
If you wish to actually view a color that represents "spectral Yellow" in as pure a form as one can get, purchase a Kodak Wratten Filter #90, and take a look at it. True, spectral yellow is not a very pleasing color, at all, and is not a color that an artist would likely consider being a representative "Yellow". It is sort a copper-y, bronze-y appearing color that one would not consider as being "Yellow" at all. However, just look at the spectral curve of this #90 filter, and you will discover that it is a quite accurate example of Spectral Yellow.
Again, this is another reason that spectral emission curves are not always a very logical way of expressing a color, unless one understands the more scientific facts of vision behind them. For example, if I were to be judging the "Yellow-ness" of a color, I'd be examining the spectral curve emissions of the Red, and Green colors, because it is THOSE that truly indicate the hue of the color, Yellow, that we will be witnessing.