There are multiple types cryoprotectants and while they are generally supposed to be non-toxic it is only to a certain extent of concentration and exposure time. Extended exposure will interfere with daily bodily functions and metabolism. So unfortunately impossible to walk around with it indefinitely. The wolverine question is interesting because some animals have evolved to have cryoprotectants for living in the arctic or surviving winters! I don't know of any mammal that can do it but I know of at least 1 frog and 1 fish species. Info may not be updated but last I checked both are being studied to study how to preserve human organs!

Hello! Not an expert in freezing and thawing live specimen but well practiced in freezing and thawing dead specimen while keeping organs and microstructures intact. The major concern with freezing biological matter is the formation of ice crystals. Water forms crystals and expands when frozen and can result in burst cells and organelles. To avoid this, we introduce cryoprotectants. These are basically antifreeze that diffuse into the cells and around it to avoid formation of crystals. It's very easy to diffuse these new compounds into microscopic specimen because the surface area to volume ratio is very high compared to humans. Very rapid freezing with liquid nitrogen, also known as flash freezing, also helps in avoiding formation of large crystals (slow freezing means more time for the molecules to align). So the simple answer is size. We can't introduce cryoprotectants into every part of a human being fast enough nor can we flash freeze a human body fast enough.