There are two reasons for this.
1) Very, VERY few people in the FGC are willing to become the teacher that it needs.
2) Most people that got good at fighting games did it through perseverence, self-study, and sometimes personal life problems. Many newcomers are not willing to do some or any of these things, and it becomes apparent the moment you tell them that they have to practice a lot.
This one hundred times. Newcomers I usually teach with my crew are excited to play Marvel and fool around with the game and ask how can they do the same things we do, as in combos. We tell them: "A lot of practice and perseverance. You won't be good at it until you ingrain the fundamentals down."
Only reason I'm decent at Marvel is cause I haven't stopped playing the game for 3 years. When I tell them that, they just get scared and walk away cause its too much work.