What's a gang leader supposed to put as a source of income? You don't know shyt about taxes do you?
Shotti is a manager so he can bank the cash he is getting of tekashi using that position as his "job" and means of income for the law. The rest of them have paper but they don't probably don't have a legal means of income on paper. You can't just bank thousands and millions in income without a means to wash it.
Cartel guys are also not just straight banking cash without moving it through other hands to wash it. Even if you go straight to a crooked bank in Mexico and throw millions in there the bank itself will come under scrutiny and might be discredited n have a hard time doing business internationally. That's why people wash their money which is easier outside the United States. Fake shell corporations and business fronts etc.
Mel and Crippy could have that cash but as soon as they try to pay a lawyer with it they gonna run into the issue of how they got it. That's evidence against them. You forgetting they was also running fentanyl. You don't just run in the bank with that cash.