If you CFI in your junior or senior year, and have say, 5 students, those 5 students can't CFI in their junior or senior and have 5 students, because the class size would have be 5 times what it was when you did it. The class size would have to exponentially increase with each "generation" of flight instructors. I've seen this model be attempted, work for a short period, and then fail. A few get "lucky", but it's not sustainable. Yes, you might be able to found some people outside of your area to flight instruct, but I don't think there'll ever be enough to really affect that situation. That goes back into a "in the right place at the right time". Not everyone can CFI and build hours that way, not because they aren't good teachers or because they don't want to do it, but because numbers-wise it can never work.