I think you’re using obsolete closed-source drivers that require external patches for each new kernel version. So the situation is entirely Broadcom’s fault.
From the Gentoo ebuild for broadcom-sta:
If you are stuck using this unmaintained driver (likely in a MacBook), you may be interested to know that a newer compatible wireless card is supported by the in-tree brcmfmac driver. It has a model number BCM943602CS and is for sale on the second hand market for less than 20 USD.


Well, Apple hardware is a bit of a footgun in general. It isn’t in their best interests for people to repurpose their old hardware (they want you to buy shiny new hardware and make them money), so they don’t exactly go out of their way to make it easy. Driver availability outside their software ecosystem simply doesn’t enter into consideration when they’re designing a product. Nor does the ability to swap out a component for something with a different chipset. They’ve been that way since the mid-1980s.