They were annoyingly supply constrained the first 2 years iirc. And the last 1.5 years or so. But for a long stretch in the middle there (like 2014-2021), not so much.
From what I remember with the launch of the Pi, I think the demand far exceeded their expectations. Remember that the thing was launched as an educational computer for schools, with a model A and B variant. At least from this article [1] it sounds like they contracted the work to build the boards out to Premier Farnell/Element 14. They originally had to do a lot of the manufacturing in China to keep the board cost low.
Eventually Sony stepped in and offered production capacity at a place in Wales UK which I think improved availability a lot.
Yeah, until mid-2021, I could reliably find the majority of Pi models in stock (usually with 10+ units) at my local Micro Center—and that was including CM4s, which quickly disappeared off the shelves and by September 2021 were unobtanium.
