At 0.1% (which still seems high) you lose out on the entrance fee but still get paid for food, drinks, memorabilia etc. Compare that to the cost for the system and the negative publicity and I'm not sure it's worth it (unless they have another motive they don't want to admit)
You’re allowed to bring in snacks to Disney parks. Pretty much any food that doesn’t need refrigeration is okay to bring. Water is free. You can absolutely ride rides and spend nothing and consume the lines of paying customers.
I imagine if you’re willing to try to get in for free or share your pass among multiple people against park rules you’re the kind of person motivated to avoid spending money.
Also, someone who makes the company money and is breaking rules is still not worth keeping as a customer. If someone spends $1000 at the Mickey Mouse gift they don’t get a pass to break other rules of the grounds just because they were profitable.