I have happened to have listened to some talks and training on county lines and gangs last year, from somebody who is an 'ex-gang member' and now works to help young people leave gangs and rebuild lives.
One of the things learned is that one tactic some gangs will use is to wait around near school gates and entice a child into delivering a package/etc for them for money, so that they now 'work' for the gang. Then they'll get them to do it again, but one of their own gang members will mug the young person, so that they have both the drugs and the money back. That young person is now in 'debt' to the gang. So they have to take more risk and deliver a bigger package, or do anything else the gang wants (and potentially the same will happen again, so that the child is falling into more and more extreme 'debt' with the gang and will do anything they ask).
County lines especially is making it easier and easier for them to earn more and more money. For some vulnerable young people, seeing peers around them flaunting cash, new trainers, girls/boys, a car or bike, the respect, the 'earning money' when they're disliking school or having a reputation there...all sorts of things, but you can see how some fall into it and can't get out.