People generally don’t take the time to learn the framework and miss out on the tooling it provides. select_related for example. If I had a dollar for every project I’ve been hired to work on that didn’t use it, well, I actually do.

Also, people in general don’t seem to be able to do more than very basic SQL, so creating views is seen as a little known performance “trick”.

In general, people who don’t read the manual.

I assume they are referring to the default behavior of the ORM fetching all fields for a model by default, and the frequent need to use select_related/prefetch_related to group your queries into larger ones that are (usually) much faster than making many small queries for related tables.