So, what the hell happened with Dragonball?

I came up with this question while watching some of the original Dragonball anime fights, namely Chappa vs. Goku, and it suddenly occurred to me that the series pre-DBZ was a totally different show. The narrative, the character development, the fights, they all seemed so much better paced, and rather believable.

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And then, out of nowhere, Dragonball Z happens, and Goku's an alien, every bad guy is an alien, and now you have to be basically a celestial being to even compete in the same league. The Dragonball Universe is notorious for the power-creep in its story, but what I'm wondering specifically is, *what caused Toriyama to throw in the whole concept of Saiyans*, and a multiverse of energy-wielding warriors? I'm not sure if he ever explained how he came up with it, but does anyone know?

Edit: Thanks to everyone for the replies! It was a serious question, I wanted to know what kind of factors might have led to Toriyama's decision-making in the narrative change, and after reading the comments, I suppose the change in storytelling does seem somewhat logical. Thanks for everyone's input!