There is nothing ‘boneheaded’ about this.
The sense of entitlement of certain folks is appaling.
And it always is used whenever a ‘big evil corporation’ does things.

GW owns the copyright on their products and the associated art.
To use these things need their permission.

This isn’t new.
It’s something fans of corporate products have had to deal with since the dawn of time.

There have only been two loopholes :
– the parody/review option
– companies not realising there was money to be had …

Why is it so damn hard to just ask for permission from the person/entitity that owns it ?
And yeah … they are going to make certain demands, because they want to ensure their art isn’t used to make them look bad.

The only thing that you could use to argue against this is the simple fact that GW kind of ripped off and copied existing tropes when they created their worlds. However those days are long gone.

There is plenty of scope to create not-40k videos and art. You just have to make it absolutely clear that it isn’t official GW and you need to be sure it is 100% your own art and not copied in any shape or form from them.

It’s easy to allow fan-art of spacemarines, because you can add enough variation so it doesn’t look like the official GW output.
With animations it gets harder as you’d have to fail the duck test on every level and constantly display a ‘not GW approved’ overlay or something equally stupid ?
So yeah … GW takes the easy route and says : no unlicensed animations(period) / end of discussion.

And think of the positive : if you do get a license then you get to use all of the GW art and design …