I think that’s one of the series that they officially mentioned they couldn’t do for LEGO because of the series graphic nature.
That was in the context of LEGO Dimensions. Where they'd be activly advertising the series, having it's brand on the packaging, and exploring the world, which would draw people to the source material. If they don't advertise it at all and don't include any branding or gorey imagery, just throw them in as one among 500 other characters, it would be fine.
I do agree that those reasons are why dedicated LEGO Mortal Kombat content is probably never gonna happen.
They really should do like, a LEGO Adults sub-series where they interact with more mature brands like MK, James Bond, and Spawn.
Actually, you know what, James Bond was another franchise they said the same thing about in the LEGO Dimensions days, but now they have a whole line of LEGO sets of Bond's famous cars. So it looks like there's a bit more nuance to it.