Yet they are fine with running microcode as long you don't update it. It doesn't make sense. Blobs don't disappear just because they are hidden in ROM.
Apparently it's OK because both the vendor and the user are prevented from updating it. Thus there's no power differential between them on that specific point.
That one kinda makes sense, because, when you can't update it, there isn't really much of a practical difference between something implemented in hardware or firmware. So not allowing blobs in rom would almost be hypocritical if you don't also mandate that the actual silicon of the chip is completely free.