Why does my elderly mom want to eat mostly sweets?

Our bodies are kind of made to crave sweets, salts, fats. Some mineral deficiencies cause a craving for sweets, such as zinc, but I would say this is more on the rare side, and your Mom could just have a craving for sweets; for me it is salt, unfortunately. I could/would eat it out of my hand! Discuss this with her doctor next visit. Some people are deprived of sweets due to pre-existing condition such as diabetes, but apparently it is myth that having diabetes cause a craving for sweets.

I have noticed this as well. My mother is the same weight she's been for her entire adult life. When we go on an outing to the market, she will inevitably fill her basket with cookies and baked goods. If she's in the kitchen looking for a snack, she'll go right for the treats and then tell me she's not hungry. It's not enough to simply stock healthy snacks -- I need to actually put something healthy in front of her and put the spoon in her hand, then she'll eat that and forget about the sweets -- for awhile anyway.

Taste buds die as we age. Sweet is usually the last flavour to go.