It's not cowardice, it's policy. Lego doesn't touch real-world present-day military vehicles like tanks, which as far as Hasbro is concerned is Megatron's official altmode. And Lego especially won't make a tank that transforms into what is basically Space Hitler. Like, Megatron's helmet is literally a polygonal-stylized Nazi helmet.
Dude's helmet is a Stahlhelm, yeah, but in fairness that was the inspiration for Darth Vader's helmet too and Lego Darth Vader exists... but then again Vader never turned into a Nazi-aligned pistol either so... yeah... it's tricky.
Like the Danes got occupied by the Nazis and Lego is a Danish company. I get it.
Okay, is it the character they won't touch, or his common alt mode? Because it was the former that prompted my response.
What's funny about Megatron from a character perspective is that whenever someone deems it necessary to give him a character beyond "Saturday morning cartoon villain" he either ends up a revolutionary who goes too far and falls into tyranny of he ends up a straight up fascist. And sometimes both.
Like IDW Megs was very clearly patterned after a mix of Lenin and Stalin who later realized his good intentions had gone very wrong and tried to make amends... a lot of the IDW 'Cons are very Soviet coded in all the good and bad ways... but then IDW has the Decepticon prison camp Grindcore. And while the Soviets had their gulags, IDW Grindcore was very explicitly Auschwitz coded. And Megatron had a few rants about organic "racial inferiority." So he's a Soviet allegory who has elements of Nazi allegory worked in.
And IDW Megs did a lot to set the tone for how he's understood going forward. Aligned, Cyberverse, TFO, and ES Megs are all playing on a variation of IDW's take.
Megatron truly is someone who can be whatever version of historic tyranny you want him to be, or he could just be evil for the lulz (which is, frankly, sort of refreshing lately after so much emphasis on giving him depth over the past two decades).
How comfortable Lego is with that may depend. They're quite happy to do Star Wars, Marvel, and DC sets, some of which are based on factions or characters with real world authoritarian leanings. The after-mentioned Darth Vader/Galactic Empire being very Nazi coded. I'm pretty sure Lego Red Skull and Red Guardian exist, to cover the right and left sides of totalitarianism.
But they don't have the added handicap of being tied to designs that Lego just won't make, period, like a Walther P-38, or a tank, or even a realistic helicopter gunship.
Like I guess they could do something like TFO Megatron with a space tank alt mode that's so clearly not a real tank it's fine... but also... this line is very G1 heavy, and they'd probably want to do G1 Megatron specifically.... who doesn't have a great alt mode option given Lego's conditions.