One of my friends is caught in a similar trap. He has been at the same company for 20 years, and his skills have degraded completely. He is a middle manager and he's been interviewing for the past year with zero success. The technology he has been working with is so out of date, no one is willing to give him a chance, and frankly, if I came across his resume, neither would I.
He is the product of getting far too comfortable early on, and being afraid of change. Once you let that sink in, then you get stuck and it becomes a self-fulfilling prophecy. I don't see him getting another job soon, and if he gets laid off, I think he's seriously fucked.
Meanwhile in 27 years, I've had over 10 jobs. I have no problems learning new technology, or jumping into a codebase and making code fixes the first day. I have a long trail of friends from all of my previous companies that I could call up and go for lunch with that day, and I still feel energetic about coding and learning the newest and latest. But I haven't been there long enough to effect change the way other long-timers have, and hence why I'm still a programmer as opposed to a tech lead or architect, etc.
I think there is a difference between longevity and stagnation. You are describing stagnation, but I don't think that is what the SA is about. When people see the former, they may assume the latter. This is understandable - people make all kinds of simplistic generalizations to reduce cognitive load but like any bias it is one you should be mindful of.
In hindsight I see longevity as a mistake - because this bias exists and it limits opportunity even when misapplied. Also I find it does take more work - or at least more attention - to stay current when you aren't being pressured by your job.
I am 20+ years in and am just realizing the truth of this perception. I knew that it was more and more acceptable to move around, but missed the memo that staying put is more and more unacceptable. If no change is 1 and constant change is 10, I am probably a 6. This is a wake up call to pick up more and more newer things. The trick is to balance staying relevant with chasing the shiny object and changing just for the sake of change. Change is only good if it is better.
It can be difficult to quantify "better". It is easier to quantify "different". If the goal is to truly learn, try the things most different from what you already know first. Even if it's not strictly better, it will be different, and it will open your mind to different ways to view problems.
I was stuck in middle mgmt after just 7 years in the industry. Although I had been at 3 different companies it still felt like a rut. I ended up going back to get a PhD in a topic I was really interested in. It worked out well, in that now I can focus on things I like. Also with the PhD employers seem to focus less less on whether you now a particular tech. Though financially it's probably a net negative.
One should interview/network for other jobs once in 18 months or so at least. It is OK to decide to stay back at the company, but doing that as an informed choice will be prudent.
He is the product of getting far too comfortable early on, and being afraid of change. Once you let that sink in, then you get stuck and it becomes a self-fulfilling prophecy. I don't see him getting another job soon, and if he gets laid off, I think he's seriously fucked.
Meanwhile in 27 years, I've had over 10 jobs. I have no problems learning new technology, or jumping into a codebase and making code fixes the first day. I have a long trail of friends from all of my previous companies that I could call up and go for lunch with that day, and I still feel energetic about coding and learning the newest and latest. But I haven't been there long enough to effect change the way other long-timers have, and hence why I'm still a programmer as opposed to a tech lead or architect, etc.