Why is the wāw in “yabḥathūna” not the circumstantial wāw?

Supplementary Practice 8: Rhetorical Analysis of Five Connected Passages

• It coordinates two independently asserted clauses
• It acts as a circumstantial conjunction before aqbala
• It marks al-ṭullāb as a substitute rather than a subject
• It marks the plural verb subject, rather than linking two clauses