Why are some cosmetics sets instead of individual pieces?


I understand most cosmetics that are sets are sets for a reason (being hard to make them separate pieces), but on some cosmetics it's just ridiculous.

The greatest example is in my opinion the Executioner, who has 3 cosmetics that are all sets. The problem is, that it's so incredibly easy to make them separate pieces! The head is clearly the pyramid and does not interfere with any of the bodies on any of the cosmetics, and the weapons are also really easily separatable.

I understand that a reason for this may be that people will have to pay for the whole skin instead of just parts of it, but why not make every skin a set then? The sole reason I refuse to buy a skin for this game, is because the skins I want to buy (for Executioner) are sets. I would still be happy to buy the entire skin for the whole price, but just make some obvious skins not sets.