Today most suits aren't black. In North America and Western Europe, at least, a black suit is considered only appropriate for a funeral and for evening wear (ie, a Tuxedo, though even for those a dark midnight blue is more traditional). In Japan black suits are everyday wear, but that is the only place I know of where that is the case. Navy blue and charcoal gray are the most accepted colors for more formal business dress, and those colors can often look black in photographs, so that might be part of the confusion.

That said, black used to be much more common in suits. In fact, the modern lounge suit (the suit that we today call the business suit or just the suit) can be traced back to a man named Beau Brummel, a former military officer who is often called the first 'dandy.' In a time (the Regency at the beginning of the nineteenth century) when men's dress was significantly more ostentatious than it is now (see this portrait of King George IV in 1816 by Thomas Lawrence: https://upload.wikimedia.org/wikipedia/commons/d/d7/George_IV_van_het_Verenigd_Koninkrijk.jpg), Brummel insisted on a relatively simple black-and-white palette, including the black frock coat which would morph into the standard men's suit. He adapted the form of his clothing from contemporary country clothing, which was more relaxed than the clothing worn in London, especially at Court. Brummel was very influential on George IV, especially while he was serving as his father's Prince Regent, and since the King set the fashion, many of those at court ended up aping Brummel's newer mode of dress. It would take several generations further for Brummel's style, which still utilized coat, waistcoat, and breeches, to evolve into the coat, waistcoat optional, tie, trousers configuration of the later Victorians and today, but the origin is with Brummel's adaptation of English country and military wear.