hi @senior-ios-junior,
The reason is that swift was released in iOS 7/8 in 2014, so before that all versions of iOS were programmed (Officially) with Objective-C.
Some of the code could be obsolete because Apple has changed or deprecated the APIs. However, with a little tinkering, you can modify the samples to run with the latest version of Obejctive-C.
Hi
If we consider the latest iOS in 2019 it is iOS 12 so I will recommend you to learn the latest technology and if you are interested in learning objective C there are ample no of books, websites and youtube resources available from where you can learn both Objecting C as well as latest iOS technologies.