Interesting question. They first originated on Trans-Atlantic Jets in the early 70's.
A pretty sharp stewardess saw the need for dishing out the food quicker, by putting roller skates on.
This was a major boost for airlines. There was a major drawback however, when stewardesses started colliding with each other and even sometimes overran the aisleway!
Another sharp stewardess took the wheels off the roller skates and pinned them under a serving tray. This was indeed the first "meals on wheels" as we know it today.
The rest is history. Hope this helps.