Entirely reasonable question. Why not mules, why not horses, why donkeys?
Tools tend to define the job. To the man whose only tool is a hammer, you know that one. https://twitter.com/escapedacult/status/1386092416990601221

2. The biggest reason I failed with draft horses is that their ideal skill set was not well suited to what my hilly land needed.
And I was *stone* ignorant. Grasping at straws of knowledge and information. Lynn Miller at the Small Farmers Journal was a beacon of knowledge.

3. What I need on this farm, more than anything else, is something to carry my stuff while I piddle around planting and pruning and observing and staking. I don't plow fields.

4. I bet I've watched this video at least 60 times.
Not an exaggeration.

5. What I want to do here is carefully observe every square inch of this 28 acres.

6. Donkeys do this.

7. Donkeys walk at the same pace as humans. Once one starts walking she'd just as soon go on walking as stop.

8. Donkeys are - this is one of those researched, somebody somewhere wrote a paper - donkeys are the most energy efficient power source, outside our own selves, that humans have access to. They can apply the most joules output per joules input.

9. Donkeys are not fast. Horses are significantly faster, even matching stride length.
Mules get speed from horses and heat tolerance from donkeys.
Plus donkeys are not horses. At all. Mules haul the army's grub and gear, but only horses are crazy enough to ride into battle.

10. Mules are (some people don't know this) half horse and half donkey. Specifically, a male donkey, a "jack" or "jackass" impregnates a mare, and the offspring is a mule, a true, sterile, hybrid animal.
If a stallion impregnates a jenny the offspring is a "hinny", not a mule.

11. Horses and donkeys don't have the same number of chromosomes. A mule has an odd number of chromosomes as a result. The odd number of chromosomes cannot divide into a viable zygote. Mules will perform breeding activity enthusiastically, but there will be no result.

12. Finally, for me personally, there is a certain "up yours" quality to my donkey-ness. In America the fast I am outspokenly slow. The least of these, my children, are appropriate for me.
And they're *incredibly* affectionate. All those videos you see of donkeys on people -

13. That's it. I hug their heads, press my cheek against theirs, pet their faces, necks, ears, topknots - pet them between their jawbones, up and down this long valley - they're lovey. I like that.
And they're not real big.
And they're not scary.
So - that's why donkeys.