Joseph: Possible explanations…
Maybe they take morning vitamins and would literally puke if they didn’t eat anything*.
*True story. I now know that I must take my vitamins with food. Or else.
Eating may also be applicable for anyone taking meds.
The person may also be diabetic and someone at shul always B”H leaves out some special diabetic cookies and cakes. You just don’t know about it.
Maybe Shabbos Shachris davening is longer and/or they won’t have time to eat if they wait.
Maybe they had a little too much wine erev Shabbos and they need to eat something just to make it through the morning.
Cake and cookies are full of sugar. Sugar can be addicting. Maybe it’s too tempting to walk by without sneaking a bite.
Some people need to eat something in the morning. Esp of they walked a distance to shul. Perhaps they basically just worked out and their body needs sustenance. It’s not the same as waking up and five minutes later walking across the street to shul, where a man davens within half an hour of waking.
Furthermore, the pedestrian commute to shul doesn’t account for the additional time it takes to look presentable on Shabbos and maybe round up the mishpacha or part with a spouse before heading off.
It could have been hours since they first got up in the morning.
That’s a different situation and nisayon compared to the person strolling in to daven ten minutes after waking up who may not even be hungry yet.