I understand the sentiment. Ill just share my experience from being at i think 8 or 9 MopedGP events.
The amount of riders is never huge, but it has dwindled, and rotated(some leave and new come in). We usually only have around 25-50 riders in total, between all classes. Maybe one of the organizers can correct me on that, but thats what it feels like. Many of us race multiple classes, but this means only 10-20 bikes per class, usually on the low end of that number. This is one reason why there is not a true stock class. Due to the nature of what our riders consist of (moped owners), there is not a ton of racing skill or money in the sport. Most often, its the only racing they have competed in. Its for fun with friends, and overall there is usually only 3-5 people in each class that are truly competitive both in mindset and skill level as a rider and builder. The rest are out there just to have fun, or are disillusioned about what it takes to win. Ultimately, just being there and going around the track is what its about, and as you mentioned, there is fun to be had at different positions in the race. Because of the vast difference in skill and bikes, the pack tends to spread out a bit. Last year, I slapped a puch together to race in the fixed class for my first time ever. I had more fun with my slower poorly tuned bike, trying to out ride and pass 5th 4th and 3rd, then hearing a real bad noise, then having to try all over again. So did all those riders. After the race we were all super jacked and reliving the moments of battling each other. If you have watched a true stock bike race (we did it in cali once) its slow as shit, and boring. In the end, I find that most people that get salty about the few guys pushing the limits of the stock class and finding fun in that, dont even show up to race, or may be more mad at the themselves for not having the money or time to be competitive. If thats the case, ya gotta keep at it, it takes dedication. I know for example Ed has been building that Derbi to be competive for like 3+ years. He also has raced for like 8 years now. Each year getting a little faster, because of all the time he puts into it.