Since photographic developers are so sensitive to oxidation, why do manufacturers almost always package them in ordinary HDPE bottles? Why not PETE bottles instead?

Finally, how important is it to keep developers away from light? I'm assuming it must not be that important if most developers are not packaged by the manufacturers in dark bottles. I'm wondering if the recommendation to use brown bottles is nothing more than a myth. I rather like using clear PETE because you can easily see discoloration.

Does anyone have answers for these two questions over which I have been agonizing for years? Ok, well not actually agonizing, but certainly curious about.