This website has a lot of data about WWDC sessions over the years. Here are some of the statistics and charts.
For unknown reasons Apple sometimes removes videos from their Developer website and app. Over the years many videos that were once available have become hard to find.
However, while a lot of videos are no longer listed on the Developer site, many are still available on Apple's CDN. Some require a login with a Developer account.
In 2024 Apple created a YouTube channel. Apple started uploading videos from the latest WWDC and are slowly adding older ones. The chart below shows how far they are with uploading videos to YouTube.
Since 2007, when the iPhone was introduced, sessions at WWDC have been about different platforms. The iPhone SDK and App Store were introduced in 2008, this is the year where macOS and iOS started to have their own dedicated sessions.
