Why is cauliflower puree healthier than mashed potatoes?

Generally speaking, cauliflower puree is healthier than mashed potatoes, mainly due to differences in nutritional content, especially when it comes to carbohydrates and calories.

Here is a comparison.

Properties of cauliflower puree:

Lower carbohydrate content. This is the biggest reason why many people choose cauliflower puree, especially those who follow a LCHF diet or want to reduce their carbohydrate intake. Cauliflower contains significantly fewer carbohydrates than potatoes.
Fewer carbohydrates usually mean fewer calories. Cauliflower is a “low-calorie vegetable”.

Cauliflower is rich in, among other things:

Vitamin C. One serving can provide the entire daily requirement.
Vitamin K
Folate
Magnesium and potassium
Antioxidants. Contains glucosinolates and isothiocyanates that protect cells.
More fiber: Cauliflower contains a good amount of dietary fiber, which is good for digestion and contributes to a longer feeling of satiety.
Choline. A vitamin-like substance that is important for brain development, learning and memory.

Properties of mashed potatoes:

Higher carbohydrate content. Potatoes are a starchy root vegetable, which gives a higher carbohydrate content per serving.
Higher calorie content. As a consequence of the higher carbohydrate content, mashed potatoes usually have more calories than mashed cauliflower (assuming a similar amount of butter/cream in both).

Potatoes are a source of potassium and vitamin C, among other things, but in a lower concentration per 100 grams compared to cauliflower.