So why are groups of stone tools often found together? Keep in mind that ancient man, when traveling, would use small temporary camps along the way. It is believed that at these camps they would leave the heavier utilitarian stone tools that would be difficult to travel with. Then consider the fact that camp sites were selected for specific reasons. i.e., near a spring, out of the wind, by an easy crossing of a water way, etc. This is why many camp sites that have been excavated are usually multi-component sites, meaning they were used by groups of people from different cultural time periods. So the same camp site by a good spring may have been used for thousands of years. Thus, over the millennia, many different tools may have been abandoned or lost in a very small area.
Last thought to ponder:
Imagine you were around back when, and you and some of your clansmen were on a trip to quarry some flint a few days away. Come evening, you would stop at a camp. Before you left the next day, you would gather the axes and tools, and pile them against a tree so you could use them on the return trip. Or, possibly it was more communal, and they were left for others traveling the same trail. Time passes, the camp is abandoned for whatever reason. More time passes, the handles rot away, and the stone axe heads retreat into the earth. A few thousand years later, the ground gets worked and the cache of axes are once again exposed. All in a very small area.