In terms of Cole and Metro... Because that's what they're passionate about. Having a good job is great, but what good is it if you're not happy with doing that for the rest of your life? I don't condone dropping out of school to chase music unless you're absolutely guaranteed to see success from it, and certain situations has placed you in that position to have to drop in the first place.
Lil Tony down the street saying he wants to drop out of school to become a rapper though really tells you a lot about the current climate of who's hot right now. Many of these rappers that are big are kids in their early 20s living extravagantly, and don't have many deep topics to share -- They're just here to make bangers and whip music, and they're fine with that lane. When you've got a bunch of kids blowing up, and you yourself are in high school cramming for that Biology test next week, of course they'll think "Well shyt if they can do it, why can't I?"
It's the lifestyle that people drop everything for, it's not for the love of music. Cause if it were the genuine love for music, they know'd how tough it is for a starving artist lmao. Kids wanna pop bottles, drive the newest cars and smoke in private jets, that's really all it comes down to. You've got some kids who do genuinely love what they do, but those rappers tend to become a Kendrick or a Cole. How many Coles or Kendricks are kicking it around in the Underground though? Not many. That's why they're where they are -- their hearts are in different places, and it always leads them to better places.