Fresh spices vs Dried spices I am new to this community and I have a question in mind.

Spices like garlic , cinnamon etc after drying lose the volatile oil content in them. [HERE, HERE]

Though We see fresh garlic in market being sold but that is not the case of other spices like cinnamon , black pepper, cloves etc.

Why don't people prefer them fresh? After all if there was a demand, there would have been supply.
Spices are generally comprised of bark, buds, fruit, seeds or stems of plants.  They are almost always dried.  Garlic is not a spice, rather, it is a vegetable, like onions or shallots.  You can, of course, get dried garlic, onions, or shallot.  But the drying process does not make it a spice.  While spices have a fairly long shelf life, they should be used when fresh.  Purchasing whole spices and grinding them yourself increases the shelf life, as ground spices, with more surface area, lose freshness more quickly.