In discussions on the intrinsic value of BTC, one often reads the claim that BTC is scarce because the maximum amount of BTC that can ever exist is 21 million BTC. However, since the "atom" is the Satoshi, rather than 1 BTC, that maximum amount is then equivalent to 2.1 peta-Satoshi, i.e., 2,100,000,000,000,000 Satoshi. Where exactly is the scarcity?
Some compare BTC to gold. The amount of gold ever mined may be roughly 200 kilotons. That is roughly 1 giga-mole, i.e., roughly 60,000,000 yotta-atoms of gold. Not all that scarce! However, it is impractical — if not physically impossible — to trade amounts of gold smaller than, say, 1 gram.
However, BTC does not have the physical limitations of gold. One cannot trade 1 atom of gold, but one can trade 1 Satoshi. Thus, where is BTC's alleged scarcity coming from?
As a total novice, the scarcity I see is in the rates at which existing BTC can be traded and at which new BTC can be generated. But, what exactly does that have to do with the number 21,000,000?