If you want to make it mandatory, then put together a constitutional amendment and get it passed.
You obviously did not even read the first paragraph of the article because it says ... “Presidential candidates now are required to file the Office of Government Ethics (OGE) Financial Disclosure Form 278e with the Federal Election Commission (FEC) within 30 days of declaring their candidacy.” That requirement is not in the U.S. Constitution. Filling out financial and national security forms are not for constitutional eligibility purposes but for TRANSPARENCY and the right to know by voters who have questions in both areas ... financial and national security entanglements of the candidates.