I used to wonder the exact same thing.Aside from wanting to perhaps own the shares, why not a CSP for the same premium with a chance to buy at 850? Trying to understand the benefit to the buy-write with the anticipation that we may go down some this week.
If we close at 845, I made $65 instead of $5 (not taking into account the paper loss on the shares). Also less margin required if using margin (don't ask me why).
Edit: If we are at 870 on Friday, the "profit" on the buy/write is $45 (can close or roll).
Edit2: The Buy/Write gives you more opportunities for more income with a roll at various strikes.