‘World Aquatics Championships’ [closed]

Solution 1:

I would say because the sports that are being competed in are "aquatics".

aquatics
noun
"2. aquatics Sports Athletic activities performed in or on the water."
American Heritage Dictionary

"(Swimming, Water Sports & Surfing) sports or pastimes performed in or on the water"
Collins English Dictionary

2.aquatics Sports played in or on water
Lexico.com (Oxford dictionaries)

2.plural in form but singular or plural in construction : water sports
Merriam-Webster dictionary

In some cases it doesn't matter whether an organization or event makes sense to us grammatically or sounds intuitive in the modern day; often the answer is something like because of historical reasons or tradition. One example is the NAACP, the National Association for the Advancement of Colored People. It was formed in 1909 when calling African-Americans may have been the norm, and despite calls for its name to be changed to reflect today's language, it still retains that name:

Its name, retained in accordance with tradition, uses the once common term colored people, referring to those with some African ancestry.
NAACP - Wikipedia

I personally think "aquatics" sounds better anyway because, as I said, and as shown in the definitions, "aquatics" is what they're doing. "World Aquatic Championships" actually sounds a bit strange to me. However something like the "International Aquatic Sports Championships" or "Games" would sound fine.

Also, a point I left out which is probably of importance, "Aquatic" is an adjective, "Aquatics" is a noun. Championship titles often call for the noun representing the sport or sports being played:

Alpine World Ski Championships
World Para Athletics Championships

Actually the ski one is probably a bad example, but the athletics one probably is in the same category as "aquatics"; ie., "athletics" refers to a number of different games.

You can think of it as "championship of athletics" or "championship of aquatics", which is how some competitions are named.
List of world sport championships - Wikipedia