3rd party lenses (Tamron, Sigma, etc.) do not use the EF-S mount style, mainly because they are made for multiple OEM bodies (Canon, Nikon, Sigma, etc.), and only Canon uses a short back-focus mount (Nikon FF bodies have a DX crop mode).
Usually, and APS-C lens will have severe vignetting on a FF sensor. Some lens designs use a larger image circle than necessary for better optical quality, which may account for the better perfomance of the 60/2 macro on FF.