TWO possible explanation.
It makes no difference if the Earth is a spinning sphere or like a spinning roulette wheel.

First possible explanation.
Many of us when we were small kids, watched in amazement when we took a small wheel (usually from an old clock) and spanned it with our fingers on a desktop. The small wheel was turning with high speed...at the beginning and it had no significant wobble. As the rpm started to drop, the little wheel began to wobble at an increased rate, then altogether stopped. The Earth's rotational momentum is getting lesser and lesser and just like that small, spinning wheel on the table, it starts to wobble more and more, before it stops spinning.

Second explanation.
When a rotating wheel is not balanced, it also wobbles. Out of balance condition appears when there is more weight on one spot on the wheel. If you think of the Earth, the weight is much higher as it used to be in China, where the population exploded. Hence, the extra number of people is the cause of the wobble.
To counter act the Earth's imbalance, on the other side of the Earth from China, extra weight is needed. The “other side” of the Earth from China is roughly Europe.

PERHAPS, this is the REAL reason for the migration that is going on in Europe. To increase the weight on that side of the Earth, thereby balancing the rotating Earth. :)
Even a small amount of uneven weight distribution causes imbalance on a rotating object.
IF, the Earth is really rotating, that is.