Yeah, because Mercedes has to assume that the average owner is clueless about oil. (which they are) They provide a cert so the owner has at least something to go by for a minimum standard for their engine. Those of us here, we know what those standards are, how the tests are performed, the (low) bar that's set for passing those tests, and how base oil blends and additive chemistry come together to define the quality of an oil. That's what we come here for. That's the whole basis for this forum.
The way in which certs and approvals are conducted makes them cost prohibitive to anyone who isn't a major additive company or global multi-national conglomerate. It costs well into the six figures to get an oil formula tested for MB 229.5 (for example) and then you're locked into that exact formula. A blender cannot deviate from that formula. So say Brand A purchases an approved add pack from Lubrizol, they must blend it to the base oil and VII specified in the formula that was used for testing. If the blender wants to add a little extra anti-oxidant to improve service life, they can't do it and keep the cert. If they want to add some ester to improve cleaning and thermal stability, they can't use the cert. Even though the oil is better with those additions, the formula used for the cert didn't include it so they can't put it in there and use the cert. It forces the blenders into a small box chemistry wise with no room for deviation. If you want to make a better quality oil, you either have to accept the indirect ceiling created by the cert or ditch the cert to make a better product.
If HPL was seeking API, ACEA, MB, VW, etc... certs and approvals, they'd have to dumb their oils way down, get rid of a lot of the chemistry that makes the oil perform as good as it does, in order to meet those certs. They're not going to do that, especially considering the vast majority of their customer base doesn't care much for certs.