Speed and scalability. Both problems are solvable, and I haven't seen anybody putting the investment to solve it in a grand scale on a popular, open source visual programming language.
For speed: it's really hard to beat the speed of data entry via keyboard. A well-designed set of keyboard accelerators would cover a lot of ground on making visual programming languages comparable to keyboard programming speed, but I haven't seen anybody pull it off yet.
For scalability, and in the sense I mean scalability of project complexity from a toy desktop project to a distributed system deployment or a low level embedded system: the vast bulk of tools that are available for supporting large projects are built around text and the fact that it's relatively easy to translate a tool working in one text-based language to another text-based language. Git doesn't care what language you're using; it's all text. Diffing tools don't care what language you're using; they diff lines of text. As tools like Copilot grow, they will start by disproportionately giving a power boost to text-based languages because they are built to work with text-based languages.
Anything that's going to work with a visual programming language in a way that is as robust as these tools do needs to treat the language as an abstract syntax tree, not a collection of lines separated by line breaks. And the tools to do that are going to have to be written almost from scratch; it's simply an underdeveloped ecosystem because there's so much fungibility between different text-based languages in terms of allowing tools that work on one to work on another.