Answer:
Because job offer is a deal between two parties and once you're appointed, you're bound to legal obligations.
Step-by-step explanation:
When you sign an agreement that is the time where you can accept or reject the offer but in case if you get appointment then you have to follow company's policy and you cannot then reject the offer easily therefore, it is important to not to accept at first hand but in case if accepted then should go ahead with the offer.