I used MAX here to pick the maximum of the net worth of the billionaires, but it seems to not work in cases like, Bill Gates, Elon Musk etc

Question

SELECT DISTINCT ?item ?itemLabel ?itemDescription (MAX(?billion) as ?billions) ?locationLabel (SAMPLE(?image) AS ?picture) ?page_titleEN
WHERE
{
  ?item wdt:P2218 ?worth.

  OPTIONAL {?item wdt:P19 ?location .}
  
  FILTER(?worth>1000000000).

  BIND(?worth/1000000000 AS ?billion).

  OPTIONAL {
    ?article schema:about ?item;

      schema:isPartOf <https://en.wikipedia.org/>;

      schema:name ?page_titleEN.

    ?item rdfs:label ?LabelEN.

    FILTER((LANG(?LabelEN)) = "en")

  }

  OPTIONAL { ?item wdt:P18 ?image. }

  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }

}
GROUP BY ?item ?itemLabel ?itemDescription ?billions ?locationLabel ?picture ?page_titleEN

ORDER BY DESC(?billions)