Please excuse my ignorance here, but are you saying that the board makers have no say on what chip they want to incorporate into their board? And those chips firmware are not open or at least accessible to the board makers?
You move off that kernel version, no BSP, no boot. sad times.
This is one reason why you don't get android phones supported past the android release shipped.
You're completely at the mercy of the SoC provider. Promises of 'n' years support are quite often quietly dropped after 18 months, when they realise all the engineers have moved to working madly to get the latest SoC's BSP out of the door.
Rinse and repeat.
Hopefully Fuchsia’s stable ABI promises pan out and companies start releasing drivers for it.
Haiku remarkably does have proper driver APIs and stable ABIs.
Linux is and will remain painful, on all platforms, until it is finally deprecated, and for a while longer after that.
As someone that has worked with these EVKs for decades, you never treated them as part of your final product. But with the advent of Beagle and RPI, that's where we are now.
But when you buy an RPi or Beaglebone as the core of your industrial smelter and expect support for that module comparable to, say, a module from Kontron? You're going to be disappointed.