I think there are 3 possibilities why they left:
1. They left because of personal reasons
2. They had to leave because no more parties possible. Not their fault of course
3. They left to join VH TV
I talk about already hiding shit which went on on loggia already. No more nudity outside bedroom or bathroom, ugly clothes Carmen wears and finally the cherry on top depressed Anita spoiling all the mood.
I do not only watch for seeing sex. Its about interaction and fun between the couples. And Zoe, Jack and Lex and Iris were simply unique in there