The TRANSFORMERS films by Michael Bay have a history of inconsistencies, nonsensical changes to concepts that used to work out better and sudden changes in not too relevant details, to the point that there's no actual need to find reasons for them:
- In TFM, Optimus Prime only uses one forearm-mounted axe-sword, in ROTF+DOTM he uses two, in AOE uses only one again (which he loses to Galvatron) and in TLK he uses a completely different looking blade that's shorter and seems to have lost the previously consistent ability to sever transformers' limbs.
- In TFM, Bumblebee was crippled and held back by the fact that he lost one and a half legs. In AOE, he dodges projectiles and is threatened by Drift with a blade (indicating that he had to prevent such damage). Yet in TLK, he just has the ability to reassemble himself like a Junkion, after shedding head, shoulders, knees and toes. This is not explained in any way.
These and some other changes just do not have "official" reasons to have occured, so it's up to the viewer to accept or to keep wondering.
My personal theories:
- They didn't use them in DOTM because the battles took place in crowded Chernobyl (crowded by the NEST crew) and later in even more crowded Chicago, and their stray lasers might have a higher range compared to stray bullets. Also, it seems that the Ark ship was weakened and thin-walled, maybe due to radiation and dust through 40+ years on the moon.
- They didn't use them afterwards because they were handheld tools of Ratchet, who died in the beginning of AOE.
TFM = TRANSFORMERS Movie (2007)
ROTF = TRANSFORMERS: Revenge of The Fallen (2009)
DOTM = TRANSFORMERS: Dark of the Moon (2011)
AOE = TRANSFORMERS: Age of Extinction (2014)
TLK = TRANSFORMERS: The Last Knight (2017)