There are cases where some companies have the business justification to work on writing their own frameworks, like with Facebook. They can use up human resources to really focus on latency at the cost of other metrics.
Other companies juggle their priorities differently, and would probably not want to focus their efforts on replacing React, which has a small API, constantly-updated documentation, a team that responds to issues, and widespread attention and thus lots of discourse. I also think the React layer abstracts away complexity, trading total lines of code for cognitive easiness. Some teams have the business justification for doing things their way -- but I think most don't.
Other companies juggle their priorities differently, and would probably not want to focus their efforts on replacing React, which has a small API, constantly-updated documentation, a team that responds to issues, and widespread attention and thus lots of discourse. I also think the React layer abstracts away complexity, trading total lines of code for cognitive easiness. Some teams have the business justification for doing things their way -- but I think most don't.