I'd say current Western popular music is saying less purely because there's less to say.
In the early 1970's there was an American culture and society waiting for something like Marvin Gaye's What's Going On, and in the mid 1970's there was a British culture and society waiting for the Sex Pistols. Even as late as the 1990's black Americans still felt the need to speak out about their lives to gain a foothold (see: Public Enemy's Fear of a Black Planet and Goodie Mob's Soul Food).
Now advances in society, partly down to some of these records and political movements that grew alongside them, mean that we're generally more accepting of other people, and apathetic about our own problems as a society, resulting in people having less to moan about. You get the odd band trying to be clever by criticising the government with tired metaphors (see Enter Shikari's 'Arguing with Thermometers'), but when the only political things to write about are the current economic climate and horse meat being used in Tesco's food it's not exactly anything to get the creative juices going.
This means that artists have to look within themselves, or their past, for concepts and ideas to build an album around. Frank Ocean's Channel Orange from last year sort of touches on the struggles he had to face when he came out as gay, and Kendrick Lamar's good kid, M.A.A.D. city from last year too was a concept album about his family and his life growing up, but he doesn't really touch on politics. Like I said earlier, the young generation are too apathetic and are more interested in dancefloors and bright lights than what goes on in the House of Commons. This is why the charts are currently saturated with dance music, and dance music hasn't ever really been "about" rebelling.
Hard-Fi are a current band that tried to battle the government lyrically, but they ended up having ideas above their station and ran out of fresh material. The same thing happened to The Enemy, only they looked to condescending metaphors about working class people to get their message across. I'll just go back to my first point; artists are currently saying less because there's less to say. The music market and the world has changed. People are now interested in catchy singles they can dance to, which is fine. But it has resulted in a lack of deep lyrical thought and ideological expression through music.
