The beavertail is to protect the hand from the slide - again, its a gun ‘for the masses’, and features like that are exaggerated.
Notice that everyone else is getting rid of exaggerated beavertails in their designs, especially in models which have a very low slide profile. It appears unnecessary and louses up the grip where the web of the hand meets the grip. I suspect someone at Sig intended for this big beavertail so as to attract the notion that since the USGI 1911 had one, the new USGI service pistol ought to have one too.
I like the modularity of the serialized trigger pack, but other manufacturers will probably improve on the design so that it’s not an obstruction to the contour of the grip.