Coasting is the norm for most people once they get past the “up or out” part of their career. There’s a lot of variance in how long that period lasts depending on the line of work, but after that for every 10 people you’ll have:
2 who work hard and are net additions
2 who actively work against things to maintain whatever they have
6 who are just content to be there, do what they need to do to continue to get paid and lean towards whichever of the above groups make their life easier at any given time.
It's kind of inevitable for coasting to be the norm. There will not only always be a majority of mediocre contributors (I don't mean this as an insult) and most companies don't provide enough incentive for excellence or pressure against slacking off. People just eventually figure out that there's no consequence to coasting, especially when the job is no longer novel to them. And why shouldn't they? The fact that we can coast at work is actually pretty great, and something that wasn't really tolerated in other times. Now we can "check out" and spend at least some of our lives doing things other than being corporate drones for our entire waking lives.
2 who work hard and are net additions
2 who actively work against things to maintain whatever they have
6 who are just content to be there, do what they need to do to continue to get paid and lean towards whichever of the above groups make their life easier at any given time.