There are many reasons but we'll only discuss a few possibilities...
When interviewing listing agents, the seller should ask, "How are you going to market my property And... any agent should be providing the seller with a copy of the MLS listing once it's listed so the seller can see and give input on what they would like changed, this would of course be more pictures and/or video.
To touch on a few points:
1. Some agents not tech savy - This is the business and it's only going to grow more technology dependent so agents should sharpen their skills.
2. Not having access to the home because of a long term renter - Listing agents should make a point and it should be added in the listing agreement that the seller gains access to the property for the agent. I do not list a property until I have the appropriate pictures and have accessed the home myself. If it's the owner in the home, this shouldn't be an issue.
3. REO's - agree with Antonio's statement and the seller (the lender), isn't involved on a personal level like an owner would be.
If it's a short term rental property, many times the agent wants to get the listing up right away and then intends to take additional pictures once the guest is out of the home. But, this should be stated in the listing so buyers and other agents know what to expect in the near future.