Good question. Personally, I usually would not bother removing them, but I think there are several possible reasons for removing the seeds.
The texture is the first thing comes to mind, remove the seeds and you will have a nicer texture and consistency of the sauce( or whatever the task). Also,the seeds can tend to have a bit of bitterness to them. And lastly, denture wearers or anyone with dental issues will usually shy from anything containing seeds. Ouch.
Now why she would throw out the pulp is beyond me. That IS the tomato. Perhaps it is more of a tv/time issue. That's my best guess on that part.
I hope you found this useful and informative.