Smart contracts don't “simplify contracts"
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Imagine that you have a contract to build a website for somebody. 50% up front and 50% when the site is done. So the key word there is "done" right? (and "done", here, can be a proxy for more specific terms, the principle is the same) A smart contract is designed to complete the transaction once the bit is flipped, but there's still the decision behind who gets to flip the bit. I.E. who decides when the thing is "done". The smart contract is not designed to deal with the ambiguity of the word "done".
So the types of problems a smart contract can deal with are those for which it is feasible to reduce the terms to binary states. Escrow is a good example. I can verify that x dollars moved into account A, so I will move y dollars from account B to account C. But the number of use cases like this are a small percentage of reasons you might want to contract in the first place.
There maybe some sort of smart contract framework that comes along to deal with the ambiguity issues, but for now, smart contract use cases are quite limited in scope.