Intact elastin in wet blue prevents relaxation of the grain layer. That reduces area. Elastase-active enzymes partly degrade the elastin to increase area and improve softness. 

Elastin is a retractile protein concentrated in the grain layer of hides and skins. Intact elastin tends to prevent the relaxation of the grain layer. That reduces the area of wet blue hides.

Due to its amino acid composition, elastin isn't tanned during chrome tanning. That's why tanneries need elastase-active enzymes on tanned wetblue. 

These enzymes partly degrade the elastin. The results are increased area and improved softness, with no negative impact on strength.  Elastase-active enzymes can also  increase the cuttable area into the normally loose belly area. That leads to an even larger improvement in area.