Why is an old iPod nano worth so much?


My son is desperate for an electric guitar, so in an attempt to gain some cash without doing any real hard work he’s gone hunting through everything that has been ignored since he got a phone and found his iPod nano 16gb 7th gen and put it up on fb mp. He put it up there as being open to trade or offers and joked that if someone offered him $20 he’d happily take it. Within minutes he is telling me that its had 36 views, next thing there’s been over 100 views and he’s had 1 offer to trade. Then the cash offers started to come in first $30 now it’s up to $70. Why do people want these old iPods so much?