Why did "Dragon Ball" (the original TV series) change from being a comedy/ecchi, to a drama? I just wondered.

Just for the record, as “comedy” I’m talking about the parts until the Tenshinhan saga, whereas as “drama”, Piccolo Daimao and Piccolo Jr.. I just wanted to know if Toriyama dropped all the comedy because the manga studio told him so, because it was already pre-planned, or because of something else. Thank you for the patience.