Some claim that the political revolutions that sprang up near the end of the 18th century spawned a desire to distance oneself from the relentless extravagance of royal court life. There are those who credit the start of the industrial revolution, with the concomitant need for more practical clothes suited to business. Some blame Beau Brummel. I suspect that the truth of it involves both these and many other unknown factors.
But the result was that the color, and variety drained out of menswear, almost entirely. A man was shortly only able to wear significant color in a vest or cravat.
Shapes and cuts kept getting more select. Options disappeared in droves. And by the start of the 20th century men were left with this.
Then, in the later 50's we had to add the growing youthquake into the mix, and the burgeoning sexual revolution. All at once the desire to dress in coat and tie began to be challenged in a significant way. Sure the suit still held primacy, and even now is still a major player. No designer would send out a collection without at least a few suits. But with the continuance of a desire for color, and comfort, the suit is continuing its slow fade into the distance. In another 50 years, possibly sooner, the suit will be a kind of specialized gear for only the most formal of occasions, like a wedding.
The vast army of gray, navy and black is being supplanted. And different ways for men to dress are emerging.
Where this is all likely to lead, who can say? I have some notion in my own head, but we have seen enough times already what happens when people try to predict fashions. The results are usually pretty funny.