A lot of developers even with multiple years of industry experience seem to start projects with code first -- as if it will be running on their PC.
Not enough systems / design thinking of how the application will run in a DEV environment (typically cloud these days) let alone production -- what the various components of that application are going to be -- and where and in form the data will be persisted.
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