I'm not here to argue with someone about what I and people I've talked with have or have not found painful or difficult. That is no one's place to tell someone what they did or did not experience.
Water fasting is not good for you. The only place that rave about it are niche wellness groups who often have no actual basis for their claims. There are obviously also religious groups who are doing it for spiritual reasons. Am I saying nobody water fasting finds it painless and peaceful? No. Some people do. But from a medical standpoint it is frowned upon because, especially in long term cases, you are malnourished. You are not receiving adequate calories, electrolytes, or nutrients to sustain bodily functions. That is going to wear you down. Many vitamin and nutrient deficiencies are associated with pain and malaise. Potassium imbalance can cause muscle spasms and heart problems. Vitamin C deficiency (aka scurvy, yes the pirates disease) can cause easy bleeding. Low iron can cause headaches and severe fatigue. If all you are consuming is water, eventually all of your body's nutrients will be fucked. So yes, pain is very possible to occur. Maybe not everyone will, I'm sure many people have played their cards right and had peace in the process, though I'm sure some of that came down to their psychological state and personal beliefs for why they were fasting as well. But starving to death can very much be painful. Emma Wants to Live is a great documentary about how it is a slow and hard death, especially when compounded with mental suffering (in her case severe anorexia).