The only well studied and clinically developed diet for people with serious irritable bowel diseases, known as FODMAP[1] focuses exclusively on minimizing specific types of sugar and carbohydrates. For a severely compromised digestive system, table sugar is likely recommended over dates as a sweetener because they are likely to contain 'free fructose' which may be fine or even better for normal digestive systems since it has lower glycemic index than glucose, but it is found to be complicating for people with serious digestion problems. This goes to show dietary sugar is not metabolically simple or equivalent as commonly thought.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952847/