They have to be big otherwise the "victim" won't be fooled easily.
This is one of the oldest methods of scamming newbies. It is either fake story to sell something like this (picture of the key/mnemonic or a wallet file supposedly containing a lot of bitcoin) to them and make money from their naivete. Or a malware embedded in the file they are giving away for free to infect the victim's computer and steal their coins instead.
Nobody would bother with such things if there were $10 worth of bitcoin in it