WITH clauses are a somewhat recent feature, at least on PostgreSQL. If you learned SQL before they became commonly available, it's unsurprising if you tend to think of other SQL techniques first.
Maybe 15 years is "somewhat recent feature". :)
So yeah, if you first learned SQL around 25 years ago, something added only 15 years ago is "somewhat recent". And according to a link posted in another comment, other databases introduced this feature (non-recursive WITH clauses) even later.