Why do 4-wheel suitcases usually have their wheels on the short side, rather than the long side?

In a 4-wheeled suitcase, there are three possible ends to put the wheels. Most commonly, the wheels are at the short end:

^{Public domain image}

I find it hard to keep them on 4 wheels; one has to push, and if there is the slightest obstacle (such as tiles), it tends to topple over.

Rarely, the wheels are at the long end:

^{Source: Bet Bath and Beyond}

I've never used such a suitcase.

They could be at the large end, essentially like a cart:

^{Source: RDM Industrial Products}

I've never seen that design in a suitcase.

Why do 4-wheel suitcases usually have the wheels at the short side, rather than at the long side, and never at the large side?