To generate interest and a great Open House.
Also, sometimes an agent does so if the property does not show well.
Also sometimes the agent is just incompetent and cannot take pictures and load on MLS.
Generally, there are requirements once you list, as to by when or how many days
you have to have pictures.
For example in Santa Clara County our Board requires pictures up in 3 days.
Call your agent or get in touch with the local board if you want to file a complaint.
If there are no requirements the, they want Buyers to come to the Open House.