Those of us who never had to buy them now have to for backward compatibility. That especially includes us iPhone people who are new to the party and have to buy both the newer standard and the older. There are a lot of iPhone people.
For anyone, you have to carry double the number of cables. You might find a modern charger or you might find an older one.
Are you asking why USB-C is more convenient? It’s smaller, it’s reversible, it carries more power, it has faster data …. How’s it not more convenient?
Imagine how much less beautiful the world would be if this face weren’t allowed to succeed