Don't pull the same falsehood crap that Aled did. Because someone uses a configuration improperly is no reason to condem the configuration, just the poorly trained diver.
Yes and no. People buy octo holders and they expect those devices ... wait for it ... hold the octo. Problem is, as @PfcAJ stated, they often do not. Add in cold water divers with thick gloves and thus little dexterity, if it comes off, how easy is it to put back on? The only octo holder I've seen work well is the necklace. Magnets work okay too. The rest? As soon as they wear, they don't hold it reliably, if they did when brand new.
We have restricted fields of view from our mask. If the octo is not at the top of the triangle, we won't notice that it is loose unless we check for it. That's just a weakness of the standard configuration.