They were discontinued along with all the other types and sizes because of slow sales.
First to go were the 18 and 20 sizes like 1618, 1718, 1720, 1818, 1820, 1918, 1920 because they were so tough(stayed straighter longer, too) that archers used them until broken. Easton found out that if they offered larger diameters in thinner walls they would break easier thus creating more sales hence all the 12, 12, 14 wall thickness sizes. Then along came carbons in 3 sizes that worked for all bows and now aluminums are much harder to find in good hunting sizes.