People in your category usually lack the motivation necessary to keep up to date on the most efficient techniques, and they'll put fewer hours in general into their craft. They'll typically produce less effective solutions as a result, because they don't know all the options and refuse to learn all relevant tools.
For a concrete example, I'm currently (hopefully for not too much longer) working at a large defense contractor with a lot of 20 year+ software developers who have never worked outside the company in an engineering capacity. Some have kept up to date, but many hang up their engineer hat the moment they walk out the door, and it shows in their work. They don't learn anything new that they aren't forced to, and they often don't care about code readability, maintainability, anything that wasn't taught in mid 90s. They don't know what continuous integration is, and they don't particularly care. They argue, sometimes successfully, against changes and infrastructure that would be no-brainers at any marginally competent software dev house. They think agile is a horrible idea because all they know is my company's half-assed, broken implementation of it. These are the people who are still writing bloated 500-line functions in new code, giving me blank looks when I mention refactoring at the code review, and approving said functions anyway. It's very hard to be fired unless you commit a security violation, so they'll keep happily churning out horrible code until they hit retirement. Then they dream of kicking their feet up in Florida (literally in one case) and doing nothing. Or so they claim. Hell they've been in the aerospace industry for over two decades, and in many cases I, the junior man, had to tell them who SpaceX and Blue Origin are and why they mattered to our industry (and possibly their jobs in the medium/long term). They simply do not care. They approach their job like they're making corn flakes on an assembly line, and our product is many times shitier than it should be as a result.
If you can't tell, their wilful mediocrity pisses me off. :P They're part of the reason I'm looking to leave, although my larger problem is with leadership, or lack thereof (imagine these guys getting promoted, where they can care even less about staying up to date). Not to paint the whole company too badly, there are good engineers/managers that I work with, and they're a welcome breath of fresh air when I do. Just far too few of them for my liking.
If your goal is to simply remain employable then fine, you're welcome to find all your fulfillment outside of work. But if your only motivation is the stick and there's never any carrot, the moment that stick goes away you're going to be passed. From the sound of it fear of unemployment is your only incentive. For the sake of your co-workers, I hope you never find an overly stable job.