It appears that the World Cup tournament was not an idea that came from Vince McMahon & WWE officials, but from the Saudis themselves.
WrestleTalk has reported that the WWE World Cup tournament being held at Crown Jewel in Riyadh, Saudi Arabia is due to the Saudis being upset over Qatar landing the 2022 FIFA World Cup of soccer. The Saudis reportedly wanted the soccer World Cup but did not bid on it and couldn't get it, so they went to WWE to hold their own World Cup of wrestling at Crown Jewel, according to the report.
The issues between the Kingdom and Qatar stretch back all the way to the mid-1990s but have escalated in the past few years as the two countries fight for power in the region.