He, or indeed she, it's hard to tell with sloths, appears to be a Maned sloth (Bradypus torquatus) found especially in the Atlantic forest, from Rio to Bahia and one of six types of sloth in South America. Maned sloths have very little muscle mass for their size, which saves weight when hanging from branches, but it does mean they can hardly stand on the ground, let alone walk. Their only means of locomotion is to slowly drag themselves along (if attacked they stop completely and lash out with their claws, which can be surprisingly effective).
But why exactly are sloths so slow? They are very, very, specialised in what they eat, concentrating on leaves of forest trees, especially Cecropia, a common pioneer related to nettles. This has pros and cons. The pros are that leaves are very abundant and easy to catch, the cons that, well, leaves are rubbish as a food. That's why so few animals eat them. There is very little nutrition or energy there, and what there is is extremely hard to digest. Even sloths, with specialised stomachs full of plant digesting bacteria can take up to a month to digest their food so that as much as two thirds of a sloths body weight can be just it´s stomach contents. With very little energy to spare, sloths save all they can. They have very low metabolic rates, and low body temperatures. Mostly they just hang in trees, using special hooked claws so that even this doesn´t take much effort.
Sloths seem to only leave the tree tops for two reasons. Firstly to defaecate, which they do one a week, usually in the same place. Quite why they do this isn´t exactly clear, though the smell might help to attract a mate, otherwise a bit of a problem for an animal that normally hardly moves. Which brings us to the second reason, and maybe the answer to our question. Why did the sloth cross the road? To find another sloth!