Because likely the deal takes longer than that to complete and you are stuck with whatever the price is on 3rd week of dec.

If the market is crushed for some reason your calls might be worth .50c or 0.00. The stock will dive in sympathy with debt mkts, indexes enough to erase your 1$...then you have to watch the deal close 50 days later. Ouch. No free lunch in arbland.

GL! AT.