Why do hashes have bigger keys than block ciphers?



I've noticed that modern block ciphers usually have 128-bit or 256-bit
keys, but hashes are usually twice as large (e.g. AES is 128, 192, or
256 bits, but Skein is 256, 512, or 1024 bits). Why are hashes bigger?
Does it have to do with preventing collision attacks?
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