It really stemmed from getting hundreds of pre workout formulas over the years and I got tired of all the packets all over my house. I have never even bought one. I just kept getting free ones all the time and just started combining them into Tupperware. Eventually I was adding bottles of creatine, bcaa's, beta alanine etc to the Tupperware container with all the other stuff already mixed in. I then realized every once in a while i would get a couple of scoops that were terrible, then get a couple that were perfect, so I started to experiment with the other free stuff I got, then evolved into what i currently do.
I actually still have tubs of pre workout pwders, but I only use them when I want my carbs high that cay b/c most of the formulas have a boatload of sugar. Most of the ones I make are sugar free, or very low