Why does the average profitable daytrader only make $90k a year?

The average yearly income for a profitable daytrader is around 90k-100k. This doesn't make any sense. You would think that someone who's figured out how to consistently win more than they lose in the stock market should be making, at minimum, multiple hundreds of thousands per year, not 5 figures. If a person has been trading for years and years and is consistently able to turn a profit why don't they start reinvesting profits, copying trades, borrowing more money to trade with, scaling up, etc. If you can make $90k a year why not scale up and make $180k a year? It's like building a working money printer and just printing $1's and $5's instead of $100's, it doesn't make any sense. Someone who's been trading and profitable for 5-10 years should have no problem going from an average profit of $300 a day to 1K a day, but for some reason most don't apparently. Obviously I'm missing something...

I've got a question for those that either are or know long-term year-after-year profitable traders that are confident in their strategy, what's keeping you capped at around 90-100k per year?