Why is YouTube not Applying P2P to Streaming of Uploaded Clips, and Live Events

I wonder why YouTube is not applying P2P to stream, it's faster; possibly because hole-punching for P2P is not 100% success rate?

P2P in streaming of uploaded videos:

• Lost package can be gathered from another viewer
• Future-in-time packages can be loaded first
• Packages can be loaded from another viewer instead of server to reduce server load

P2P in streaming of live-event videos:

• Lost package can be gathered from another viewer
• Future-in-time packages can be loaded first
• Packages can be loaded from another viewer instead of server to reduce server load