While sloths are slow – indeed, they are the slowest-moving mammals on Earth – they are not lazy. Sloths move at such a lethargic pace to conserve energy, something that is in limited supply due to their herbivorous diet. This comes as all species of sloth are native to the Americas and spend the majority of their lives hanging in jungle/forest canopies, eating any leaves in their immediate vicinity. Due to this severe absence of fats and protein, they have little energy to tear from tree to tree. Simply put, sloths have evolved to best exploit their environment and increase their chances of survival.
Answered by HIW.