Base sizes being changed perhaps? As it happened to the Grey Knight power armour units just a couple of weeks ago.
They Wolf Guard and GK Strike Squad are both on 32mm bases. Not sure if GK were on 28mm before or not.
GW did 3 pack sizes. 5 man for WG, 10 for the standard Wolf Pack and 15 for Bloodclaws.
It wasn't an official boxed set and wasn't good value compared to the standard box so not sure if many even bought it.
I doubt there's anything behind this change to be honest
Not sure what you mean it wasn't an official boxed set? It was a group of 5 Wolf Guard which is a official pack and sold on official GW store.
As for Value it offered more weapon options per model than the 10 and 15 packs. It also fall directly in-line with price compared to the 10-pack and 15-pack at roughly 12-13 USD less per 5 models, but you keep more weapon options as you go down. See Below.
10-pack=37 USD (13USD less than 15-pack)
5-pack =25 USD (25USD less from 15-pack, and 12 less than 10-pack)