Lack of water for ablution or suitable clothing for prayer raises questions about the way a duty may be fulfilled, not necessarily whether the prayer duty still exists.
Under the appropriate legal conditions, tayammum can replace washing when water is unavailable. Clothing-related incapacity is likewise considered under rules of ability and covering.
The distinction: some recognized conditions remove a particular duty, while others change how it must be performed. These consequences must not be merged into a single rule about hardship.