Darwen and Date tend to be pedantic and don't focus on things shops actually care about. They spend far more time on chalkboards than in the field.
Plus, SQL, or a variant of it, can be adjusted to fit most of their complaints. That would be more practical than entirely throwing out an established standard and starting over again from scratch.
Again, I have gripes about SQL also, but something typically has to be significantly better to replace a standard, not merely somewhat better. And the SQL standard can be adjusted and expanded as new actual lessons are learned.