Why is there always a tournament?
In the medieval Era, tourney season would happen, true... but not in Japan; It only happens in poorly constructed CCG games and badly written Weeb RPGs that don't consider what Japanese words mean.
But even then, tournaments didn't have a set schedule, there was just a high likelihood near spring planting and/or fall harvest for a couple hundred (out of Three Thousand) years.
So... not common.
In any culture.
Except in every single fantasy and isekai manga!
WTAF