Why did they design new connectors for USB?
Most likely many reasons, at least the following.

It was a requirement for the connector to support hot-plugging. The connectors you mentioned do not support hot-plugging.

Using an existing connector also means it is possible for someone to plug in two incompatible devices together just because they use the same connector.

The connector also needs to support enough mating cycles to be usable.

And the connectors you mention are old, as technology to make connectors advances, it makes sense to use that technology to make a modern connector that is smaller and more durable and otherwise better, and most importantly, a connector that is suitable for the specific application.