Basically it’s because every situation is different. Many times it has more to do with how well they read and studied the information before ordering. Some don’t install it inside their cushion cover and just lay it under the cushion. Following the 3 easy steps to learn how to do this is so important in achieving good results. The case studies are also a valuable tool for pre-determining your results.
Your results vary depending on your measurements. Most of the time it’s just a matter of simple math. Your cushion height and your before sag measurement determine your results. Measuring sag depth while sitting the actual way you sit is very important. You must have at least 2” of remaining foam height while sitting in order to have enough foam density left to compress and add firmness.
Of course this can’t work at all if your spring deck is damaged, severely weakened or broken. In that case nothing can work except repairing the spring deck.
This issue is so complex and there are so many variables to consider, that it’s not for everyone. For some it’s far too confusing and for others they understand exactly what we are saying and are able to get great results and delay buying new furniture. That’s just the way it is.