Then it may be that the agent does not have personal photos of the interior and there are copyright regulations about using photos of others. The agent is offering to help you lease an apartment there, but does not necessarily have the complex management's permission to use existing property photos.
If it is a privately owned property where the available unit is still occupied, then it may be as you suggest, the tenant does not want photos of personal belongings made public.
I agree w/you that is would be more helpful to see photos of the space available, a floor plan...something other than the pool, parking lot, etc.
Great question. I wish there was a better answer, but it is usually because these are the only pictures provided by the complexes. Personally, I don't post ANY pictures on my craigslist ads anymore and they do ok. I used to post as many pictures as I could, and honestly speaking, it was a waste of time.
I'm glad you put this out there, because I have often felt the same way. Being on more than my share of apartment tours, I often roll my eyes when they tell me about the weight room that no one uses, the community center that's deserted, and the jacuzzi that looks like it's been abandoned for three years. When given the option, I always tell them to skip that part and just show me the unit. Much like on the guided tour, photos of these items are draws to get you to sign the lease. Nothing more.
Sorry for my rant.