Hi ckp,
The simple answer is money, marketing, profit, and the ability to claim “proprietary” designs that use lower quality and less durable materials which can’t be compared to other mattresses and which need to be replaced more frequently that drives the larger companies which control the majority of the industry (whew … hows that for a single sentence :)). Latex is much more common with smaller manufacturers that recognize its value and are more focused on customer satisfaction than profit margins or shareholder or investor returns.
This would be a preference and depend entirely on whether the mattress provided you with the PPP (Pressure relief, Posture and alignment, or Personal preferences) you need and prefer. As you can read in the first overview here … the two basic functions of every mattress are pressure relief and alignment and everything after that is preference. The marketing that has led people to believe that thicker is better has allowed the larger companies to put a lot of inferior materials in their mattresses and sell them at inflated profits based on this single belief. It’s the same belief that has led people to buy so many pillowtop mattresses over the last decade that “feel” good in a showroom but that fail so quickly because of the low quality foams they use in the comfort layers or buy mattresses that are overkill in terms of what they need and then wonder what happened when they develop soft spots that lead to the loss of comfort and support but the impressions are still “just below” the warranty exclusions. If you need some extra softness in the mattress to provide you with better pressure relief then you could always add 2" of softer latex over a firmer 6" core but with careful testing your body will tell you if this is necessary.
If you test the mattress carefully on the same or similar foundation or box spring that you would be using at home then the answer to whether you need more latex would depend on whether it provided “enough” pressure relief, “enough” support/alignment, and had a “feel” that you liked. If it doesn’t then you may need to look at a different design that has thicker comfort layers to provide more pressure relief. If it does then there is no need to use more latex. You can read more about the potential benefits of a thicker mattress in post #14 here.
Phoenix