You were a inexperienced beginner finding and exploiting tens of bugs over a 10-15 week course. In between other courses and learning you only had hours to maybe a few days per bug. On Zerodium [1], a generic Linux LPE pays 50 K$. At normal experienced exploit developer costs that buys you ~200 person-hours. That is professionals spending 10-100x as much time as you spent.
Just think of the gap between the first time in the woodworking shop and a carpenter, first time pottery versus a master, a new painter and a professional artist. Think of how many things the master can do that it is literally impossible for the new person to do. Then add another 10-100x as much time on that. That is the gap.