I'm in the audio hardware industry, and the answer is clear. Yes, being a no-growth company is a big reason, and yes, they're incredibly selective of their new employees. And they're a stable company, which helps. Go to NAMM, ship products to retailers, design next year's product, repeat. Incredibly stable.
But they have ups and downs just like every other company, which at best follows the trend of the industry's economy. There are two options a company will do to cope with this situation.
1) Lay off X% of their workforce, shielding their existing employees from the financial "downs".
2) Lay off 0%, increase the workload of everyone to account for the financial losses, and see who quits.
This is incredibly common in the "tech arts" industries like pro audio hardware because their employees can easily find better paying (2x) jobs elsewhere but choose the audio industry because they're following their personal dreams. They're much more willing to make large sacrifices at their job, so they are less adverse to leaving if their boss says they need to hammer out 120 cymbals a day instead of 80. And of course some people quit and often decide their dream isn't worth it anymore. It's a bit easier for the company because there's less paperwork when someone quits, and they're guaranteed to keep their most passionate employees (by the algorithm's design).
To hire more employees during the financial "ups", they just continue their campaigns that working them is the best job ever despite the low pay, because well, to some wanna-be-cymbal-builders, that's the truth. Imagine loving your Zildjian cymbals since you were 7 years old, finally with the opportunity to work for them when you're 20! (fine print: 46 hard hours at $28k/yr)
Nothing's really bad about this. It's just high supply and low demand of workers, so I'm not saying one method is better than the other. I'm just trying to offer my view on the topic of the article, since the actual article fails to address their own question at all. (The only near-answer I in the article is that the employees aren't fully replaced by automation but instead moved to other jobs, but come on, how is Zildjian different from the other tens of millions of jobs in America that can't be replaced by automation? This is hardly the real reason in Zildjian's case.)