With the rise of MTV (and to a lesser extent, Much Music here in the GWN) and the Music Video, pop music became as much about the aesthetic as it did the selection of a beat and style that would resonate with your average listener. This is where the Gaga/Spears/Perry schtick comes into play with the theatrics, background dancers and the like. Yes, the comments about it somewhat relating to old school burlesque are not off the mark, sex sells.
If you look at early efforts by more traditional style bands in terms of fitting into the MTV framework, Metallica's video for "One" is an example of what they came up with:
You'd have the band, doing its thing, while alternating to dramatic scenes or content related to the lyrics. The band itself wasn't partaking in the cinema, the producer was trying to add a visual element to the music. This got better with time and some bands would put themselves into the theatrics and then carry this over into their stage presentations. Rammstein is a fantastic example of that, their concerts are pure theatre.
Another thing that really took off during this era was the girl/boy band. Backstreet Boys, NSYNC, Boys 2 Men (sp), TLC, New Kids on the Block, Destiny's Child...etc. Unlike with legacy bands where there were instruments being played by the members, this was all computer generated background music where all the members participated in singing and dancing, and it was this style from the start, there was no adaptation curve, the visual component was a key facet of the band's "style", because a large part of their exposure would be through TV.
Through all its phases, pop music has never been about complex music and deep lyrics. It is catchy, typical simple in both music and lyric and is not meant conjure up deep emotion or profound thought in the listener. This is what has proven to appeal to the general population and is easy to market, creating a "brand" out of the artist who may not actually be all that talented, but is somebody who you can sell the image/presentation of.
Now of course this is not always the case, Lady Gaga is actually a classical pianist, who was quite good, but that was never a genre that was going to elevate her career. Jennifer Lopez is extremely attractive, despite not being a great actor or singer, and she's had very successful careers in both due to her appeal. Amy Lee from Evanescence has written some very deep, introspective songs about her personal demons (battle with depression and the like) and these were pop hits, despite the band not really catering toward the pop genre. Metallica's Black Album is one of the most successful of all time, having numerous hits despite it also not fitting the pop mold. There are these exceptions that transcend the "rules" of pop and put bands with legitimate talent in the spotlight where the public is eager to consume their material.
As a listener, I have a penchant for deep lyrics and heavy music. I grew up listening to Metallica and memorized and analyzed their lyrics. I was introduced to Nightwish by a member on here and immediately fell in love with them for the same reason. I want a song to make me think and make me feel, mindless garbage drives me nuts which is why I avoid rap, hiphop, pop, most country...etc. Of course not all of that music is trash. Tupac Shakur was a gifted musician who wrote some excellent lyrics, but you don't have material like that being produced today and becoming mainstream like his did.
Probably one of the best examples of bad pop is the Alanis Morrissette song "ironic", where, ironically, the events depicted were not in fact ironic. The song became a hit regardless of that fact because Jane and Joe Average aren't even aware of that being the case, and so it doesn't bother them. That's pop in a nutshell.
Best explained facts I have seen put in writing on the subject.
