Why do numbers exist? We needed to describe amounts; we needed a common language to talk 'amounts' in.
"I want this many coins for that many sheep."
Now, coins and sheep are easy. It's kind of hard to trade in half living sheep. Dead half sheep, now there's a different matter entirely. But still, two parties agree on a standard amount to trade in and from there on it's a matter of counting.
A container, this big , filled with grain, or butter, or wine, is counted as 1, etc.
This is also why zero was an unknown in the west until well into the middle ages. Why would you want a number that represents nothingness ... "there are no cows in this pasture, how many coins will you give me for that?"
Ever seen the Roman numeral for zero? The Greeks and Hebrew used letters and assigned them numerical values ... which is where the number of the beast, for instance, comes from. The Babylonians too had no concept of nothingness. They wrote their number pretty much like we do, except, in stead of 0 they left a space. So 206 was written 2 6. Easy enough, right? Except that 26 and 260 were written the same. You had to tell the difference through context.
Zero had to be invented, just like the wheel.
You might as well ask how we account for roundness. Why is it that round things roll while other shapes, at best, hobble along?
Are amounts a purely human thing? No. As an impromptu experiment in my kitchen showed. Dogs know when the number of treats they get is too small. But dogs don't have a language for amounts. So numbers are purely human, right? Well, no, bees can communicate distances. A distance is an amount.