k-means: Only one-dimensional cluster predictions in two-dimensional space
KMeans does correctly do what it is supposed to do.

Just plot your data correctly, with the same scale on both axes...

Y deviations do not matter, they are tiny compared to the X axis. Deviations there are 100x larger, so squared deviations even 10000x. Since KMeans minimized squared errors, only x matters

When plotted correctly, your data more looks like this: