I'll just speculate based on my own experience and a little of what I read here. Many people start vaping looking for the throat hit they got from cigs. PG gives you throat hit, VG gives you a warm smooth feel. So newcomers are often relatively high PG and also high NIC, the nic partly because they need a lot but also because it gives additional throat hit. Personally I was never looking for throat hit, even in my early days of vaping but I think I was unusual with that, just from what I anecdotally read.
As people get more experienced with vaping they tend to evolve into a smoother hit, especially as they upgrade to more powerful gear. A strong throat hit at 50W is a lot different than a throat hit on a CE4. So I think there is a *tendency* to evolve into a smoother vape. These are generalities of course. Just sort of an anecdotal statistical thing.
If you are interested in DIY you will find it well worth it to look at the DIY section. The pinned topics are a good place to start although you may already know the basic safety issues. It will save you a lot of trial and error. A really good juice, like the better premium commercial juices, blend a primary flavor (a fruit or whatnot), creams, and sweeteners. Most flavor concentrates are not designed to be used alone. They are intended to be components of a more complex mix. For instance, fruit flavors usually do not include sweeteners, it is intended that you sweeten to taste. You can add things to a mix but never take away, so that philosophy makes sense. This is particularly true of TFA (The Flavor Apprentice) flavorings, which are very popular here. There are exceptions and you can learn that in the DIY section. Anyway, by following published recipes you quickly learn how 4-9 different flavorings interact. It would be very difficult to reinvent that wheel by yourself.
