The Thundercats 4" got clearanced first because of how bad the case ratio was and what was on the shelf district/region wide. There was no moving the Mummy Mumm-Ra and the Lion-O/Tygra 4"
Its about how much money you are going to lose, the "cost" to retail of the 4" is negligible. Meaning it can be lost, the vehicles and bigger items (Armor of Omens, Tower of Omens) are going to sting more with their loss.
If you ran a store and did not clearance the 4" you would be looking at a situation where you make no money vs making a tiny bit of money. You are going to lose either way, so at least put a band aid on it instead of let it hemorrhage
The Mezco items don't get clearanced because that is a different contract with a different vendor, its apples and oranges. Stores can keep that on the shelf longer because its a niche item that usually holds its value instead of decreasing. You don't really see the Mezco Mumm-Ra going for 1/4 of its price on eBay and in speciality shops. The 200x MYP Roto's were the same type of deal, I can still get $50-100 for each one if I wanted even though everything else in the MYP line has flatlined.