Consider the alternative where a bigger number of modded boards with dubious RAM gets into circulation, which is no problem for Chinese companies to do. It would quickly result in a distrust of all RPi products and everyone would suffer.

It also has nothing to do with going public, it is consistent with what they were always doing: it never was fully open, in fact quite the opposite and they were always protective about their HW, you can't even order the SoC as a separate chip, only as a part of premade/customized board.