Lamar Jackson's mother is his representative. He's not going to have any problems with endorsements. Your talent will bring in the money. You don't need a swindler like Boras and Rosenhaus to be your mouthpiece. If athletes feel comfortable giving away 5%+ of their hard earned salary, more power to them.
That's great... Not everyone has a support system/family they trust to handle these types of things. I'd argue in most cases it's bad business to have a mom, dad, whatever negotiate a multi-million dollar endorsement deal or contract. But there's obviously exceptions. I'd never trust my parents - or anyone without experience managing negotiations at that level - to do the dirty work in negotiations.
Basketball is a lot more straight forward. Contracts are what they are, maxes, opt-outs, it's all pretty easy with just a couple decisions for the player. NFL contracts would be a nightmare. MLB's tough because there's no max, usually all guaranteed, but there's a ton of deferrals and other **** that go into negotiations.
These agencies are also a lot of the time managing money and helping with investments and budgeting and all that ****, too.
If you got a good support system/structure around you,
maybe it makes sense. In most cases for most of these athletes, it absolutely doesn't make sense.
Boras and Rosenhaus are out here doing silly **** because it gets them on TV and gets them in front of future potential clients. It's free marketing for them. Nothing more, nothing less. They're not doing anything any other sports agent isn't doing on that back-end.