Why were animals in the ice age era so much bigger than the animals today

Not all animals were large during the last glaciations, but some were. A big animal has a smaller surface area in relation to its volume, so it looses heat more slowly than a small animal would. Looking at things another way, why don’t we have many big animals today? Humans are very efficient predators and they will hunt larger rather than smaller animals, as you get more meat. So we are left with a world populated by mainly smaller animals.