There is no problem with that, as Bitcoin itself will never reach the transaction volume of regular cash - it couldn't even handle that given the number of transactions (nor does it make sense to store your coffee payment on any given day for a lifetime in the blockchain). Thats where layer 2 solution such as Lightning come into play - for everyday, more privacy-friendly smaller transactions that are not put on the blockchain. And on Layer 2, you can go even smaller in denominations.
To reiterate and paraphrase: "we need more coffee shops to accept bitcoin" "but it's not divisible enough" "that's fine because we don't need coffee shops to accept bitcoin"
Well to be fair, Lightning IS bitcoin - and inevitably tied to it. It is just a different protocol, or a different mean of accounting and transferring ownership of bitcoin.
Just imagine Gold was used as money, but you quickly realize that weighing and dividing gold is cumbersome. So someone creates a layer 2, prints green paper bills in arbitrary denominations and that very someone guarantees you can exchange those green paper bills at a fixed rates for ounces of gold. You exchange green paper bills, the green paper bills have value, but the underlying asset still is gold. Until that someone decided no longer to do the exchange to gold for those green sheets of paper, and basically performed the first rug-pull in history. That is where bitcoin steps in, as its decentralization guarantees there is no such rug-pull. And lightning is the green bills that can be exchanged for the underlying bitcoin anytime, without relying on the promise of a third party.
