Being a programmer as a hobby, I can say that eight to ten hours of programming can get quite tedious. Adding some fun into a program is somewhat relaxing. Granted, this does not justify it. Secondly, the programmers realize that they are not taking up a huge amount of resources and that users enjoy them. Probably the biggest reason that programmers add their names in secret places is recognition.
Authors get their names in magazine articles and even encyclopedias.
They are authors in their own right and deserve just as much recognition as writers. Easter eggs may be troubling to corporate heads, but are great fun to users. More importantly, they help give the programmers the recognition they deserve for their efforts. I am glad Apple retracted their decree. I can only hope that companies will start to realize that Easter eggs are not the problem, the lack of recognition is.