Is there an in-universe explanation for why Transformers suddenly started using guns instead of transformed parts of their bodies?

In the first 2 films the Transformers transformed parts of their bodies into guns (for example, Bumblebee and Ironhide are seen in closeups doing that. Also the cube-infected items do that). In the 3rd and 4th films, all of a sudden, they use handheld guns and swords (in 4 we see them running out of ammunition for the first time, even) instead of transforming parts of their bodies like in the first two films.

Is there any in universe explanation for this (aside from the script writers suddenly finding hand held guns and swords cooler after 2 films not using them)?