It's possible that this note at the bottom of the article was not there when you made your comment: As a note CTEs at this time are an optimization fence in Po

It's possible that this note at the bottom of the article was not there when you made your comment: As a note CTEs at this time are an optimization fence in PostgreSQL, though there are hopes of that changing in the future. Common Table Expressions are an incredibly useful tool for reporting. At times the readability of CTEs outweighs the performance impact, but consider the trade-offs when using them