As the market goes down, which strike do you intend to sell?
If you get assigned at 290 and then you sell a call at 300, you're good for that month but what if your shares reduce to 250.
You can sell 300 again but it won't be worth as much.
Then market goes down to 230, what do you sell.
If you sell close to the underlying then you could be called away, locking in the loss on your shares.
That or you have to roll up each time it gets close.
Yes, that's the issue. The option selling strategy works best when the underlying doesn't really move so you can keep selling the same strikes month after month. In reality, it does move. Options are not a stand-alone trading strategy. They are tools to exploit an expected move.