To project "eternal" power and combat growing public boredom, Nazi plans for future Nuremberg rallies centred on massive architectural expansions such as the 400,000-capacity German Stadium for "National Socialist Games" - a permanent replacement for the Olympics.
The Nazis intended to counter the psychological fatigue and diminishing enthusiasm that, by 1937, saw many citizens view the repetitive, quazi-religious rituals as increasingly mundane.

Hitler - the approachable visionary of a New Germany (as suggested by propaganda images)
Historians note that the regime relied on a 'constant state of experience' to keep the population mobilized.
Without new military victories and grander spectacles, the repetitive nature of the rallies would make it difficult for participants to maintain the same 'emotional peak'.
Possibly by 1938 the rallies had reached their 'emotional peak' and were destined to be a 'thing of the past'.