The value of loyalty programs, for the customer, tends to inversely correlate to the state of the economy.
In very broad terms: tourism is a larger part of the travel market than business travel. When the economy is bad, fewer people travel for pleasure, and those who do don't fly as much. So loyalty programs ramp up the rewards for the people who are still flying, in order to hang onto them. Then when the economy recovers and tourism picks up again, there's less need to desperately keep customers by any means available, so loyalty programs start getting slashed.
On top of that, at all times the big US airlines tend to hand out redeemable-only miles like candy (elite-qualifying miles are the ones that are hard to accumulate¹), which makes them a heavily inflationary currency and requires jacking up the redemption rates every so often to soften the blow of all those outstanding miles.
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¹ Airlines in the US issue two types of miles. Redeemable miles, usually abbreviated "RDM" in the frequent-flyer forums, do what the name implies: you can redeem them instead of using cash to purchase a ticket. They offer no other perks. The other type is the "elite-qualifying mile" ("EQM"), which can be redeemed for a ticket but also contributes toward qualifying for some level of "elite" frequent-flyer status with the airline. Elite status is what gets you free upgrades and free checked bags and all the other perks.
Elite-qualifying miles, with very few exceptions, can only be earned by actually purchasing a ticket, getting on the plane and flying (sometimes this process is also referred to as "BIS" -- "Butt-In-Seat" -- miles). All the "50,000 miles for signing up!" type offers you see with credit cards are denominated in redeemable miles, for example. If you know your way around the loyalty programs, you can generate hundreds of thousands of redeemable miles per year without too much effort. Achieving 100k elite-qualifying miles in a year, however, is a significant feat and typically qualifies you to the highest public status tier (the big three US airlines each have at least one unpublished tier above that, offered by invitation only to customers perceived as extremely high-value).
In very broad terms: tourism is a larger part of the travel market than business travel. When the economy is bad, fewer people travel for pleasure, and those who do don't fly as much. So loyalty programs ramp up the rewards for the people who are still flying, in order to hang onto them. Then when the economy recovers and tourism picks up again, there's less need to desperately keep customers by any means available, so loyalty programs start getting slashed.
On top of that, at all times the big US airlines tend to hand out redeemable-only miles like candy (elite-qualifying miles are the ones that are hard to accumulate¹), which makes them a heavily inflationary currency and requires jacking up the redemption rates every so often to soften the blow of all those outstanding miles.
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¹ Airlines in the US issue two types of miles. Redeemable miles, usually abbreviated "RDM" in the frequent-flyer forums, do what the name implies: you can redeem them instead of using cash to purchase a ticket. They offer no other perks. The other type is the "elite-qualifying mile" ("EQM"), which can be redeemed for a ticket but also contributes toward qualifying for some level of "elite" frequent-flyer status with the airline. Elite status is what gets you free upgrades and free checked bags and all the other perks.
Elite-qualifying miles, with very few exceptions, can only be earned by actually purchasing a ticket, getting on the plane and flying (sometimes this process is also referred to as "BIS" -- "Butt-In-Seat" -- miles). All the "50,000 miles for signing up!" type offers you see with credit cards are denominated in redeemable miles, for example. If you know your way around the loyalty programs, you can generate hundreds of thousands of redeemable miles per year without too much effort. Achieving 100k elite-qualifying miles in a year, however, is a significant feat and typically qualifies you to the highest public status tier (the big three US airlines each have at least one unpublished tier above that, offered by invitation only to customers perceived as extremely high-value).