We have better abstractions for textual programming because there has been much more research poured into them, but there's nothing preventing visual languages from being used at higher abstraction levels - they don't necessarily represent the computer circuit level.

The typical strongest point of visual languages is that you can represent relations by proximity. This way, you can directly indicate the connection between a caller and its calles with an anonymous connector line, whereas in text you would need to declare a variable name, pass it as a parameter and assign it to a local variable. This makes moving data between components much more verbose in text than in graphs.

Textual programs try to approximate this relations-by-proximity with indentation levels, but the expressive possibilities in a visual language are stronger. This makes them also more difficult to lay out and organize, though. But I foresee than in the future, better support in IDEs will make it easier to mix visual and textual languages.

It is worse than that: we have 100k years invested in language and 5k years invested in writing language down. Pure visual communication went out of style with the cavemen and was never very effective beyond being used as supplementary material.

Visual has some large advantages as well as drawbacks. It uses a different part of the brain for reading that works more in parallel, and can actually augment your short term memory. However, making visual work requires taking advantage of its concreteness, which textual language styles can't do very well.

I think textual programming languages predates visual languages on account of the hardware available at the time...