http://www.people.com/article/jennifer-aniston-justin-theroux-wedding-matthew-perry-matt-leblanc

Perhaps she didn’t want her wedding to turn into a Friends reunion of all six cast members?

It's understandable. Just because you've worked with somebody, even for a long period of time, doesn't necessarily mean you'll be lifelong friends. The show ended 11 years ago. I'm sure there is no ill will between any of them, they just haven't all maintained a close relationship.

They all seemed very friendly & cordial to one another, it's a shame she didn't invite them. Maybe she had to trim the guest list and just couldn't fit them in.