Large mammals were not, in fact, hunted to extinction. Archaeologists have understood this since the '90s, although Wikipedia has still not caught up.

The North American megafauna, 30+ genera strong, were wiped out by the end-Pleistocene comet strike that caused continent-wide wildfires 12,800 years ago, as recorded in Antarctic and Greenland ice cores. This comet strike coincided with the beginning of the Younger Dryas cold spell, and is suspected of causing it. North America at the time boasted giant sloths, mastodons, mammoths, dire wolves, camels, horses, saber-tooth cats, and beavers, bison and bears much larger than what is left. Their fossils mostly appear right up to the continent-wide black mat of platinum-enriched soot, and not above it.

So those remaining of people who had been making Clovis spear points were obliged to shift to hunting the smaller game that remained, and made the smaller Folsom and other projectile point styles after. The continent-wide uniformity of Clovis points before the strike may have been a consequence of their status as trade goods, where deviation would reduce their value. After, the trade networks may have been disrupted, or maybe smaller points were easier to make, so were less valuable to trade. Most questions will probably never be answered.