First issue: low contrast. Since you have only your colours to create the form, if they're not clearly distinct from each other, then the form is not distinct.
Second issue: no shelves! The edges of your shelves make it look like bars on a window or something, since there are no visible shelves beyond those edges.
Between these two issues, with the lack of shelves and the low contrast, it reads like a stylised window rather than a 3D cupboard.
Nitpicks: the curves on the bottom two shelves are sharper than the curves on the top, giving it a look less like stylised curvy perspective, and more like bent shelves. The curves overall are rather jagged, which isn't helping the read.
Here's an edit to add shelves and tweak and smooth all the curves (and outside edges a bit) and colours:
In addition to changing the values of your colours, I also hue-shifted them and progressively reduced their saturation the darker they are. If you keep your colours the same hue and saturation, you get a very boring result. Shifting each darker colour (or lighter colour, for highlights) towards some hue makes the palette more interesting, and adds a sense of ambient light in the scene. Similarly, changing the saturation makes things more interesting, and adds a touch of realism. If everything is equally bright (saturated), then nothing feels bright, everything feels dull! By reducing the saturation on some of the colours, the others feel more saturated and colourful.
Lastly, I merged some redundant colours you had. One of those, a separate colour for the shadows in the top left, was probably a mistake. The other was the colour of the fronts of the shelves, I merged it with the colour of the fronts of the walls, since it's very similar, and since those surfaces are facing the same way and are at similar enough depths that they should be about the same colour unless they're different materials.
I'd add some shadows to the shelves the further back they are, I opted not to do this so that you can more clearly see the shelves.
Have you tried adding doors on the bottom cubby? Stand-alone cupboards like this often have some.