It's not so remarkable that he was carried off by some infectious disease in 1850, which killed a lot of people. Perhaps more remarkable is that he survived as long as he did during his military career, which began in 1808. During his service, he suffered yellow fever, dysentery, malaria, and assorted other fevers and sicknesses -- the lot of the pre-modern soldier. As president, he spend much of the summer of 1849 ill with severe diarrhea and fever, and the nation feared for his life at that time. So the 66-year-old Taylor wasn't in the best shape by the summer of 1850, and Washington City wasn't a particularly healthy place to live in those days.
Taylor left behind one of the notable what-ifs of presidential history. Would he have supported about the Compromise of 1850, as his successor, President Fillmore, did? And if not, what would have happened? An early attempt at secession successfully suppressed in person by President Taylor, as a commander in the field, that would ward off disunion for a generation? A bungled military attempt by the president that would ensure Southern independence? Something else not involving Taylor's military experience?
July 9 is also the day, in 1896, that William Jennings Bryan gave the speech that made him famous and won him the first of three nominations by the Democratic Party for president. For more on the "Cross of Gold" speech, see March 19.