This is a topic that's interesting to me.
Rap is one of the few genres where how someone became famous is such a focus. In any other genre, it's automatically regarded as a lucky break or because of talent. In rap, there are so many things that go into it.
But, to really think about it, it is more than just social media cross promo.
In actuality, it's a mix of a few things:
1. Good Branding
2. Consistent music quality
3. Relatable subject matter whether through catchiness or image or an amalgamation
4. Proper cross promotion
5. Everything setup so that once attention is caught on one platform, it goes between various means of social media on different channels.
Most rappers have awful recording quality. They spend $5 on a youtube beat, $6 on mixing and recording, and then $3 on a cover and expect their music to have traction. Great quality is one thing, but artists like Shiloh Dynasty have an easier go because all they need is a guitar, an instagram channel, and a good aura.
Rap, is hard to stand on its own. Artists like Boonk (or whatever his name is) blow up from shenanigans. Others blow up from their vibe or their ability to shitpost. I imagine you have to pick your strengths, make your weaknesses as much as non factors as possible, and systemize your process as much as possible.
There's a reason why artists like kanye west drop an album with 30 people on the credits. It's because its a melding of minds and resources to drop the best product possible, whereas in other genres one guy takes credit for everything even if he had help (I have worked with studio clients before and I hear horror stories). Rap does this as well (especially to producers) but its alot more open with how they get where they get.
The more control you have over the details, and the more you invest time and energy wise into each release from its creation to polishing to distrubtion, the more potent your ability to make am impact will be.
Because, all in all.
It's just business mate.