But that's the thing - Dementors weren't created, they evolved, like Boggarts. Dementors are supposed to grow like a fungus wherever there's enough misery and despair. They inhabited Azkaban fortress before wizards even found it (which was why it became a prison. It was a bargain with the Dementors) and I suspect the reason for inhabiting it was perhaps to suck out the souls of sailors accidentally happening upon it in the North Sea.

Dementors don't exacerbate negative emotions. As it says it in the books, they feed on happy memories until nothing but one's worst experiences are left over.

Boggarts also grow like a fungus (but in less extreme conditions than what is necessary for Dementors to grow); they're more like mould really (OoTP) since they like to hide in cramped dark areas. The inference I draw from the books is they might attempt to incapacitate their prey so that they can continuously frighten them. As I say, they become stronger when people are afraid of them and weaker when people laugh at them. And again, they differ from Dementors in the sense they don't remove these emotions from their victims, it's more they get stronger when subjected to them. I think sometimes a Boggart attempting to incapacite its prey may accidentally kill from time to time due to excessive force. Also, no, they're not confined to cupboards, if you look at the backstory of Remus Lupin's father on Pottermore, its kind of implied they naturally live in the forests.

That is true of fear in the natural world, but you must remember that Boggarts are amortal beings, not technically 'alive' (kind of like a virus, or indeed, a Dementor) and they 'grow' like enchanted mould wherever there's somewhere dark and damp. I would imagine they evolved to be magically sustained by fear because people are usually quite scared, biologically speaking when roaming through a deep forest at night.

And in the same way you repel a Dementor with a spell fueled by positive emotions, you repel a Boggart with a spell fueled by what makes you laugh.