Why are procurement teams constantly transforming?

A bit of a generalisation with the title, but it always seems that procurement teams are going through, have just finished, or are about to embark on a transformation program. Why does procurement seem to be ever changing? Do other parts of the business go through the same and as frequently, but we just don't hear about it, or is procurement guilty of this? I believe that being adaptive and responsive is a good thing, but do you think that sometimes procurement cannot deliver what it is promised, or is supposed to, because of an ever changing landscape?