The dreams that they see reflect the deepest desires of the Demon Slayers, which are ingeniously fabricated by the Lower Rank One of the Twelve Kizuki, Enmu, to keep them in a vegetative state long enough to destroy their spiritual cores located in the subconscious.
In just over six years Demon Slayer has become one of the biggest fictional franchises on the planet, and certainly one of the most popular in Japan.
This means that some episodes are less productive than others, but it helps the series find its voice more quickly as a result.