Coupon question

Silly question but I have been couponing my entire adult life. It started back in the 80’s as a hobby and also a way to spend time with my mom on a Sunday morning while we cut out what we were going to use for our weekly grocery shopping. Back then the cashier would give you back the difference in cash and my mom would always let me keep it. Fast forward 40 years later couponing is way different than it used to be. Now there are coupon fairies that you can purchase multiple inserts from but my question is how on earth do they get so many inserts to sell? I did my fair share back in my younger days of extreme couponing but I would do coupon swaps and trains, meetups and clubs to get multiple coupons. How on earth are people selling 100’s lol?