Why did Al-Daraqutni choose to favor irsal (discontinuity in the chain of narration) over wasl (continuity in the chain) in his critique of Al-Bukhari and Muslim, even though the addition of a trustworthy narrator (ziyadah ath-thiqah) is acceptable?

The issue of conflict between wasl (connected transmission) and irsal (disconnected transmission), or rafʿ (elevated transmission) and waqf (suspended transmission), is a matter of ijtihad (independent reasoning) among the Imams of Hadith. It relies on the circumstantial evidence surrounding each hadith, and there is no fixed, consistent choice in this regard.

Al-Daraqutni's preference for irsal or waqf over wasl or rafʿ is not an act of stubbornness; rather, it is the result of his ijtihad based on the available evidence. This is a common practice among most critics, as they often prefer the "deficient" (disconnected or suspended) over the "excessive" (connected or elevated) because it is common for trustworthy narrators to make errors of addition in the chains of transmission, and deviation from the norm may indicate the deviator's meticulousness.