I have certain free ticket codes from HDFC, ICICI and Amex but since last few months whenever I try to purchase a ticket using these codes, the availability vanishes. Even in cases where ticket is being booked 15 days in advance and prices are just around rs. 5-6k levels.
Only availability using these codes I can see are where fares are very low and the free value represents only about rs. 500 - 1000.

Is this the case with others as well? Have these free codes become a marketing gimmick now?