Whilst this suggestion is a joke, last time I checked scrap.tf had too many hats and not enough metal to buy any more because they were full with the robot hats

people who buy for 1.22 or lower are quickbuyers so people who are looking for quick metal will sell to quickbuyers under market price

because no one buys craft hats for 1.44 (what's the point if you're only saving a scrap) and the 1.22 buyers, while sometimes successful, are mostly outweighed by the people who buy for 1.33 (scrap.tf included). also, plenty of traders will accept craft hats as a substitution for 1.33 refined.

in an open market, businesses (traders, in this case) who buy a good that is relatively common buy it at the highest price they can that still allows them to turn a profit - if they don't buy at that price, someone else will, and these businesses are usually looking to acquire a high volume of said good (craft hats are no exception to this - the more you have on hand when an update makes a new hat craftable, the more likely you are to get a low craft # hat).

but wait, couldn't people buy craft hats @ 1.44 refined and still make a profit as compared to the refined metal crafting recipe? indeed they could, however, it seems to have not played out that way. perhaps it is because 1.33 is easy to add up and doesn't require you keeping scrap to complete transactions.

of course, all of this is my own hair-brained speculation, and i am in no way qualified to give a definitive reason as to why craft hats are 1.33, but there's my guess.