I've also argued in favor of that; I don't actually like Pis personally, but they're a super common, cheap enough, easy to acquire system and that's huge.
Well unless they want to target PowerPC and make interested parties buy a Raptor Talos workstation what else is open enough for you? (Actually I would support this) Are there RISCV systems that are blobless?
I don't know where this idea that the RPi has good hardware documentation comes from. One glaring example is its DWC USB controller. Sure, it has a Linux driver that is open source, but its datasheet is not publicly available!
So if you want to develop your own driver for it, you have to second guess its documentation by reading at the driver's comments. This is bad.
What do you mean by documented? Sure we have a general idea of how stuff works, and some implementations can even serve as a reference but almost nothing is documented in an official sense. Your average Chinese SBC is much, much better documented, in the sense that the SOCs are at least officially documented. The Broadcom soc isn't.
I think the replies to this post may be missing the point? AIUI The raspi CPU drivers being closed makes it actually pretty hard to write an open driver for it. So you would need raspberry pi or their CPU supplier to write the driver for you, which they wouldn't do for a small OS. It took multiple years to support raspi 4 in mainline Linux and AFAIK raspi 5 still does not have a fully functioning mainline driver. That's why Raspberry Pi OS exists. You would pick a CPU that has open drivers because it would be easier to write your own for a different operating system.
Sure, that's one of the reasons I don't like them. But AFAIK that's not an impediment to running a custom OS, so I think for a lot of projects the tradeoff is good.
It's not so much the proprietary blobs, as the complete lack of documentation and debuggability for the peripherals. The PC platform, and several other SBCs, are either well documented, or at least give you the possibility of obtaining hardware with documentation.
That, combined with general flakiness (eg, power delivery issues for peripherals on older pis), and you end up with users blaming the software for hardware issues.