Few reasons come to mind

1. MIS vs CS

Management Information Systems vs Computer Science, in general people with background in MIS are more into Databases than CS people

A person with MIS background is more likely to start with an ERD, and move to code later, CS people prefer to code first

2. UML is a disaster

Since the 90s UML is the Diagraming language and it never had a DB component (probably created by CS guys) (you adapted a Class diagram for ERD)

And UML is not code, and its hard if not impossible to code in UML

Its a lot easier to go from code to diagram and diagram to code for ERD, not the case for other types of coding

I think the rise and failure of UML played a big role in coders not diagramming

3. Code browsing tools

Code browsing tools are usually good enough for most coders, seing the structure of your code as a tree on the left pane of your code editor