You may be following the letter of the law but not the spirit of the law.
The cashback was created as an incentive, you found a way to exploit the business model for personal gain in ways that can have an impact on others ability to enjoy the system while having a material impact on the provider of the service. Most in your position will say "but I am only a small piece of the cog" however, if a small minority starts to think the same way, it can have a real impact on a variety of things, including trust between parties.
Everyone tries to rationalize their actions, whether it is or becomes socially acceptable is another matter.
Well, everyone that takes a VC subsidized ride on Uber is also having a negative impact on their business. If the business makes rules that are unsustainable for their business, it’s their fault. They could very easily set limits to curb abuse.
Uber are obviously trying to get people to use their service. If using their service is bad for them, that's their fault because they were deliberately trying to encourage a behaviour that was detrimental to their business.
That is different from finding a way through the rules which is clearly unintended.
The best way I've seen businesses get around this issue is to just have an upper limit on the incentive like interest applies only to the first $x. Its often a nice bonus for people that were going to use them anyway but not enough for people to justify exploiting the incentive alone.
The cashback was created as an incentive, you found a way to exploit the business model for personal gain in ways that can have an impact on others ability to enjoy the system while having a material impact on the provider of the service. Most in your position will say "but I am only a small piece of the cog" however, if a small minority starts to think the same way, it can have a real impact on a variety of things, including trust between parties.
Everyone tries to rationalize their actions, whether it is or becomes socially acceptable is another matter.