Why is my Craft button labelled "Special"?

Solution 1:

The Special tag appears on this menu button while a limited-time offer is available. When you open the crafting menu, the third tab out of five (a leaf) is selected; select the second tab (a leaf within a 12-pointed star) to see these offers. If no offer is currently available, the Special tag will presumably be absent. (At the time of this posting, the offers are Tom Nook's chair and K.K. Slider's stoll, each available for 250 leaf tickets.)

As specified by Anthony in the comments below, the special tag will still show up even if you buy each of the items currently available.