How certification can still be relevant a decade into your career.

Certifications provide a structured framework to learning. Something to learn and something to measure that knowledge against. It isn’t about the designation - these people have been in their career long enough that the actual certification itself won’t make much difference to their resume. Instead they are leveraging the certification process as a way of structuring their learning. 

Certification objectives cover features of a product that you might not be aware of if you purely seek knowledge to complete a specific task. For example, you might have taught yourself how to use System Center Configuration Manager so that you could use it for operating system and application deployment. You don’t bother to learn anything more about the product because you haven’t got time to dig deeper and you don’t have any reason to learn it. If, on the other hand, you were looking towards a certification in SCCM, you’d have to learn about all aspects of the product, not just those that were OS and application deployment related.

Certification gives you a goal. Although people might pick up a book on a particular product hoping to learn more about it, most don’t get past the first few chapters because there is no structure to their learning. Think about it this way - when you buy a textbook about a product you use, do you read it from cover to cover? Or do you just go to the index, find the page that solves your current problem, and then put the book back on the shelf? Certification gives you a reason to broaden your focus on a product. A reason to learn about those aspects of the product that you don’t immediately need. Setting a goal that you can accomplish can make you more motivated to learn than just saying to yourself “I’ll read this book and then pick up another”.