Some time around 1990 pop music changed. Before then people would write lyrics, and write music, and find a match to combine the two. In the 90s most pop music was the music, the beat and the hook, with some lyrics tacked on. Vocals became just another instrument, they were not really there to convey an interesting message.
It took at least 20 years to really get away from that.
The 90s were not a good time for music, and neither were the 2000s... The cost of producing music fell dramatically, but that meant a lot of badly produced music was getting released. The previously high cost acted as something of a filter.
As for rap, you have to learn to appreciate it I think. Good rap songs have some really clever rhyming and lyrical structures.