Why are these so rare?

Only recent valid sale:

Sold for 10 pure + ~3 keys' sweets

http://backpack.tf/profiles/76561197964171516?time=1446710400&compare=1446796800

10 + 3 = 13

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Unusable sales:

Sale 1:

Bulk for an Ancient Duck (bulk, should be used on the Duck)

http://backpack.tf/profiles/76561198085993070?time=1447574400&compare=1447660800

Sale 2:

QS'd for 10 pure

http://backpack.tf/profiles/76561198085993070?time=1449216000&compare=1449129600

Sale 3:

Sold for an Electrostatic Cyborg (outlier due to QS)

http://backpack.tf/profiles/76561198069260201?time=1447660800&compare=1447747200

11 X 0.9 = 10