Canada

I am not saying it's obvious, I am refuting the suggestion it's arbitrary and not understood… you not knowing the reason for something does not imply the reason is unknown to all

The vast majority of travel visas are denied because Canada can't verify something about security or ties to the applicants' origin country… "cup-related" travel has zero mitigating power over those, if anything it makes things worst

You’re suggesting that it’s obvious why world cup-related travel would result in a larger fraction of visa applications denied than other travel? It’s not to me.

Compared with normal times, the world cup sees a much bigger proportion of people applying for tourist TRVs compared to work and study permits, and perhaps these have a higher rejection rate, which leads to a higher rejection rate overall. There is also the fact that the demographics of who is applying for world cup visitor visas may be a higher risk population than those who usually apply. In terms of the disparity between different countries themselves, this is quite normal that countries with higher risk of visa overstays, illegal work, etc, will have higher rejection rates.

Refusing visas and determining admissibility is an act of sovereignty, I don't really see anything here worthy of an investigation.