I think looking at some simpler models may make more sense to begin with.
Firstly is understanding search engine economics; you are the product if you are doing the search, the people paying are the advertisers.
Secondly, all rewards systems never provide a 1 to 1 ratio; if you think of any rebate/rewards system, the rewards are often 1% back of your spend. So just consider that for a moment, Air Miles, Gas Rewards, Credit Card rewards etc, company 'loyalty points' for a job well done (even these you pay significantly more in point conversion than buying it retail). You just flash your Air Miles, and you are given miles, and yet Air Miles is extremely profitable until they found no one was spending them, so they made some adjustments there.
If you are spending 10 minutes a day searching every single day and some for other things, you need to consider the amount of money MS is profiting from advertisers just based upon what you are 'seeing' not even counting on what may be clicked. I should be clear, most people are not likely spending 10 minutes a day searching Google. We use Google when it's necessary, you are voluntarily using Bing 10 minutes a day, the search engine looking at random stuff!
You have no insight into how much profit is being made, so you think you're walking away with a steal, but 10 minutes a day every day is likely worth much more to them than you are getting back in rewards to MS. Quite frankly, you are likely not receiving a favourable ratio; if you think you are gaming the system after years of many folks doing this, you are wrong.
They know when the system is being gamed, they make changes. I had access to lucrative employee discounts for Xbox products and they fixed that up within 3 years. Believe me, MS ain't dumb. They didn't become the largest market cap in the world letting people 'game' the system. They let the world pirate their OS and software for years and they are still on top.