That doesn't help if you're getting several Citi no-AF HHonors cards a year. They're already no-fee cards, but just how many can you collect? You have to start cancelling them after you've had a few, or else you can't get them any more ("you have too many Citi cards open").

Perhaps you've never churned a "frequently" churnable card before. What techniques work for one-bonus-a-lifetime cards (Amex personal now) or one-bonus-only-every-few-years cards (Chase, for example) may not work for one-bonus-every-few-months cards (some from Citi, for example).

Also, techniques like converting rather than cancelling tend not to work forever, if you keep on getting more cards from the same bank, due to limits that each bank has on how many cards they're willing to let you hold.

So while converting rather than cancelling might be great for someone starting out, or someone churning very lightly, it doesn't tend to be a useful technique for people who churn more heavily and/or have been churning modestly for many years.