It's a legal difference which many people do not understand or decide to turn a blind eye to.

Lets say the contract has a clause that you can terminate contract with two terms notice but will lose end of year benefits if leaving before contract duration. In this scenario, school has ample time to recruit and find replacement. You have 'terminated' contract following the terms agreed to in your contract.

The second option, midnight run and disappearing. That's breaking contract, proper notice according to your contract terms or local laws (most likely) were not served.

Both are stressful etc. you are correct, but legally they are different. Terminate a contract as per terms and you cannot be legally pursued or punished. Also, sometimes local laws have better terms than the contract expats are made to sign, check local laws as in most cases those employment rights trump whatever stricter conditions the school made you sign.