I have often wondered the same thing myself, guess it depends on the circumstances for each operation.  I know of one operation where the father and 3 sons crop several thousand acres.  Do the work themselves and do a great job.  Another operation farms more acres than they do with mainly hired help and not nearly as good a job. 

There is a point where economies of scale ceases to be an advantage,  In fact, in some instances, one can get so big that they are losing money through expansion.  This leaves us with speculating on the reason for doing something that does not make economic sense.  Could ego have something to do with it? 

The thing that troubles me about this unbridled expansion quest by some is it makes it virtually impossible for smaller operators to compete.  Rental rates are many times driven to obscene levels by the big operations competing for more land.  We continually hear about the plight of younger farmers not being able to rent land and a big part of it is simply because of this.  The Walmart's of the farming world are driving out the smaller operations and will continue to do so.  This will also impact supporting businesses such as farm supply stores as the bigger operations bypass them in their fertilize, chemical and seed purchases.