On the other hand it makes sense if you just need to borrow their infrastructure for a while to calculate something. A lot of scientific computing isn't happen

On the other hand it makes sense if you just need to borrow their infrastructure for a while to calculate something. A lot of scientific computing isn't happening continuously, and a lot of it is one time experiment or maybe couple of times after which you would have to tear down and reassign. Another fun fact people forget is our ability to predict future is still pretty poor. Not only that, we are biased towards thinking we can predict it when in fact this is complete bullshit. You have to buy and set up infrastructure before you can use it and then you have to be ready to use it. What if you are not ready? What if you will not need as much resources? What if you stop needing it earlier than you thought? When you borrow it from AWS you have flexibility to start using it when you are ready and drop it immediately when you no longer need it. Which has value on its own. At the company I work for we found out and basically banned signing long term contracts for discounts. We found that, on average, we pay many times more for unused services than whatever we gained through discounts. Also when you pay for the resources there is incentive to improve efficiency. When you have basically prepaid for everything that incentive is very small and is basically limited to making sure you have to stay within limits.