They haven't been impossible to find, but the last year's gun sales have pushed many more people to buy spare magazines.
In addition...
Glock 'parts kits' and 3D printed or "80%" frames are extremely popular if you diverge even just slightly from mainstream.
But what rarely comes in a parts kit is a magazine.
The magazines have been selling like crazy for the last couple years, and only now has demand started to taper off with the introduction of two new 3D printed designs that are reliable and fairly rugged. All they need, that can't be printed, is a spring.
Between the places that I tend to hang out and "watch the crowd" lately, I see about 5-6 new Glock frames per day, and 8-10 other 3D printed frames (such a the FGC-9 and Mac Daddy). Each one of those usually results in 3-4 magazine sales. And that is from a member base of just 2,500 people.