>>11441302
For one, Megatron being a gun in the first place was more a matter of circumstance than them commiting to Megatron needing to be a gun. They were looking for a toy around the same size as Battle Convoy/Optimus, with similar accessories that would make it about the same price point and sized box as Optimus.
Gun laws since the 80's require a colorful tip on toy guns- but most major toy companies opt not to reproduce realistic fun, or use realistic gun colors, because it's bad optics if a toy is tied to an accident where a kid is shot for playing with the gun or threatening to use it as a weapon. allegedly the laws got even stricter so it's harder now to even leave it just the tip as the colorful part.
While they could make another gun Megatron, it'd need to be even more colorful for Hasbro to consider it Saleable- like this 2016 release which is the last Hasbro gun Megatron release.
Takara has to deal with no such laws in Japan- however they generally opt to make any gun Megatrons they have collector's toys.
Basically, it's more important to Hasbro that Megatron be a silver robot than him being a gun.