It seems to me that insurance commercials are almost always comedic. Not just comedic but absurd. Mayhem? Flo?

I found this article that explains the change that GEICO brought about in 1999 with the Gecko. Seems like it makes sense, except that if it is simply generational or that something serious needs humor, why didn't we have across the board commercial genres for other industries at earlier dates? Or did we?

So, to the question. Why certain industries and not others developed commercial styles across the breadth of the industry?

A second question. Why did some industries see the two (or more) industry leaders developed different styles that they have entrenched for decades? For example Coke as "traditional" and family with Pepsi as edgy and popish (I couldn't help myself).

Caveat: While the commercials that led me to this question are post-1999, I am interested in trends in television and other forms of advertising prior to that date.