To validate the 'favourite loadout, never changing it' behavior that makes some newer players so hard to deal with in skirmish. (hopefully not)
To make choosing ammo easier - upgrade greased, use it on most guns, upgrade burst, use it on most of the rest, retire from thinking.
To allow more/easier use of the buffing tools by making upgraded mallet/wrench a replacement for spanner + mallet. (this one is i think a good thing)
It is i think i heard somewhere intended that they will need to be earned at some point and will be able to be re-assigned.