EDIT: You can see the bottom of the Woolly World amiibo on IGN’s video preview. It is sewn to the figurine through a patch, which makes it rather sturdy. However, after three days of constant handling (and the possibility of someone just trying to take the figure), Nintendo did not want to risk the NFC chip getting out.
Although the Yarn Yoshi amiibo were available to view and touch at this year’s E3, Nintendo did not allow attendees to hold amiibo in their hands, or see the bottom of the Yarn Yoshi amiibo. Many of those that wanted to hold the amiibo were rather perplexed by Nintendo’s decision. According to one of our sources, we now know why this decision was made.
Rather than be firmly attached to the Yarn Yoshi amiibo, the NFC chip is reportedly sewn into the yarn under a patch. Nintendo feared that a member of the press or an attendee would attempt to remove the NFC chip, steal the figurine, or that the NFC chip would fall out on its own after so much handling.
Currently, this is unconfirmed, but it would make quite a bit of sense!