Trap and rap music has completely overtaken pop on the charts as the most popular genre by far since around 2017, but was already creeping its way into charts around 2015. To understand the question of how trap music got into the spotlight, lets see how pop became dethroned:
Mainstream pop music has always been somewhat formulaic, but people still gobbled it up in the mainstream, but even the biggest trends die down eventually. Mainstream pop music has become very oversaturated and bland after 2015 in my opinion, but many people argue it happened before or a little later.
When trap and rap took over, people every single year keep questioning “is this peak trap?” Everytime that someone argues that peak trap has happened, the genre either reinvents itself with a new sub genre, or a really good album. When drill music died (aka chief queef era) people thought that trap would die out, but along came the atlanta rap scene, which is still the most prevalent today. When the atlanta rap scene died a tiny bit (but not really), along came new ideas of the florida rap scene. Even today, new artists are reinventing the genre with newer sub genres such as emo rap and metal rap. The trap genre will constantly reinvent itself until it gets stale eventually.
When it comes to the question of “when will it peak and decline,” I think that trap will not peak any time soon, but will have a lifespan that is shorter than pop’s overall. This because trap music still isn’t as palatable as pop music. Most old people don’t listen to trap music, the themes usually dont click with many people (drugs, violence), and the use of language that isnt safe for kids; compared to pop where everything is squeaky clean and ready for everyone to listen to. The only thing is i think that if people continue to uplift artists with absolutely no talent, people will start to see whats up and they will get tired of quicker than expected.