Why did St. Thomas Aquinas leave the Summa theologiae incomplete?

St. Thomas Aquinas left the Summa theologiae incomplete because he died on March 7, 1274, while traveling to the second Council of Lyons.123

While his death ultimately prevented him from finishing the work, it is also noted that he had abruptly stopped writing in 1273. This decision followed a profound spiritual experience he underwent during Mass, after which he reportedly described all of his extensive written work as being "like straw". Because of his death, only the first 90 questions of the third part of the Summa were completed by him; the remaining sections, known as the Supplement, were later compiled by others using his earlier commentaries on Peter Lombard’s Sentences.41