There are many "cryptocurrencies" that have vastly more number of transactions than visa. They aren't being bought at the same rate and therefore don't have the same market cap as Bitcoin. The market has chosen Bitcoin as their favorite, because it aligns with the wants of the free market. The free market wants secure distributed and _trustless_ store of value. That's the thing that Bitcoin does better than anything.

Also you can transfer any amount in a single transaction, so the transaction value throughput in Bitcoin is still infinite. This makes Bitcoin useful as a secure settlement layer for other systems.