apparently what Keith said is ““If it’s in D&D it has a place in Eberron” – it’s up to you if you want to put it there.”
One of the core principles of Eberron is that you should make it your own. People often say “If it’s in D&D it’s in Eberron,” but the actual quote is “If it’…
keith-baker.com
So no, it is not exclusively not in Eberron because the DM ‘desired to exclude it’, as you put it. It can also not be there because the DM did not desire to include it, i.e. it simply was never added rather than actively excluded. Which isn’t really all that different from how it works in any other setting
Your statements are identical in the context of Eberron.
The GM not wanting to include it,
because of how Keith Baker structured it,
is completely identical to the GM wanting to exclude it. There is zero difference with Eberron, unlike any other setting, because it was specifically
built to be maximally inclusive. Everything, literally 100% of anything
officially published for D&D, has a place in Eberron UNLESS the GM decides otherwise.
Like look at the very words of the thing you're claiming to quote (bolding added for emphasis):
"You
don’t HAVE to use abeil in Eberron. But
if you want to, it’s a simple matter to add a lost city of bee-people in Xen’drik, to make them the Mourning-warped inhabitants of a Cyran city, or the latest creations of Mordain the Fleshweaver.
It’s up to you to decide if the Sovereigns still exist or if divine magic is another form of sorcery.
You decide the cause of the Mourning. And so on."
The one and only thing responsible for the presence or absence of ANY officially-published D&D material in Eberron is the GM. You don't get excuses there. It's completely, 100% on you. No one and nothing else prevents the inclusion of anything, and no one and nothing else prevents the
exclusion of anything.
Whatever is in your Eberron game, it is
unequivocally because you, the GM, chose. You can't
hide behind any excuses, because the setting was written so that such excuses do not exist. Period. Nothing that is officially-published for D&D can ever be excluded because it is somehow a violation of "setting consistency" because Eberron, despite being very much its own setting with clear rules and clear world-building, was written with the very specific intention that no one could ever be told "well that doesn't really
fit in Eberron, sorry".
Everything (first-party) can fit in Eberron. Everything. He even says that himself. “If it’s in D&D it has a place in Eberron”. The one,
and only, reason why a thing in D&D would not appear in Eberron is because the GM intentionally avoided taking advantage of that place.
Again: for (nearly) any other setting, this would not be true. Choosing to exclude would in fact be different from choosing not to include. Eberron is (nearly) unique in that it was built, from the ground up, such that choosing-to-include is identical to choosing-not-to-exclude, and choosing-to-exclude is identical to choosing-not-to-include. They are equivalent
because “If it’s in D&D it has a place in Eberron”.