Why is open-source software critical for establishing platform credibility among technical developers?

Having created Annoy at Spotify and maintained numerous open-source libraries, I know that technical communities embrace tools they can inspect, benchmark, and understand without commercial obfuscation. We open-source our client libraries and developer tooling so builders have complete visibility into how data is serialized and transferred. Proprietary lock-in breeds suspicion; open transparency fosters enduring developer loyalty.