So like, if you had a companion with you when you interacted with the fallen satellite at the Mohave Drive In, what reason can you think of why they wouldn't have been dragged along with you to get brain-scooped and go through a buncha wacky misadventures in the name of science?

New Vegas kinda just auto-fires vanilla companions with no explanation or reaction.

Well with the first two DLC's, you had temporary companions in them, so obviously they wouldn't want you to have your own companion. Also, the DLC's tend to be more story driven, centering on the player's character. Lastly, if you want a "game answer", the teleporter may have only been able to take the player to Old World Blues because of the different "brain grooves" as a result from being shot in the head. Thats how you're different than all the other Lobotimites. Hope this helps satisfy your questions

Yeah, I agree that a companion wouldn't fit in the first three DLCs so far and that a companion would've been turned into a drooling Lobotomite if they had indeed come along due to their lack of the special brain grooves, but that the player character turned out to be okay was a bit of an anomoly/surprise for the Think Tank and Mobius deduced that it was probably because of the bullet hole. So they wouldn't have been searching for this brain groove anyway

I'm probably just too nitpicky. The whole DLC was a bit off, imo. None of it really felt like it fit with what I understand about the Fallout universe. Trying to logically explain my companion's absense from Big MT when there really is no explanation.
Just the way it was.

Companions would've had limited survivability against the unstoppable death machine that is Big Mt on hardcoe, and would've given you too much of a combat advantage on regular.

Not looking for a game-design reason
I mean storywise.
Why would the companion have been overlooked by the Think Tank when they were bringing the Courier over to Big MT to scoop out his/her brain?
Wouldn't they rather have had two brains to scoop out?

They weren't dumb/curious enough to touch the satellite? On that note, it would be nice if they were surprised as hell when you come back alive from Dead Money or Old World Blues and acted like they thought they were never going to see you again.

DMs start was stupid, raul and rex would have been knocked out just like me or if not then they would have dragged me 2 safety before Dog/God showed up.

HH was better because of the whole 1 spot left 2 fill thing.

OWB's was the best IMO because of the force field thingy, i just think my companions would have seen the force field and backed away.

Another thing ro note is that the DLCs are designed to be separate from the game. A small game contained within another game with its own world map. So they cannot actually interact, leading the inclusion of companions being impossible. Though I have seen evidence of people sneaking companions into DLCs...

If their knocked out to, they wouldn't be able to stop Dog from dragging you off. And its possible Dog could have been told to take the one with the pipboy.

Cass went to sleep, in the town of Novac (too much whiskey, I told her to slow down). Boonehoward (as I refer to him) thought, the sole reason I brought
him to the middle of the Mojave Wasteland was to cut his throat (literally).

Well, in the technical view, it doesn't make sense that they didn't go with you. When you interacted with the satellite you were teleported to the Big Empty your companion would probably go with you. But for gaming purposes they can't go. Simple as that.

Isn't this a perfectly reasonable answer for why they couldn't come with you? I mean, teleporting one person away before their friends can do anything seems to be a staple of those kinds of 50s sci fi films.

I didn't really much like the idea of teleportation in New Vegas to begin with. It seems too farfetched for the Fallout world, I think.
But maybe if it was anything like a Star Trek transporter, they have to focus a transporter lock around the satellite or something.
Can just assume your companion was off to the side a bit, maybe examining the weird eye being projected on the big screen and was therefore out of range of the transporter beam.

Maybe because companions have boundaries? Sure they may follow you to their death, but following you with a teleporter; that's taking it too far!

Well, it wouldn't have been their choice.
It was the player's choice to go to Big MT to check out the area and enjoy the DLC they paid for.
But it was the Courier's intention just to check out this satellite's weird midnight showing.
The Courier probably had no intention of getting dragged of to a hidden research facility and having his/her brain, heart, and spine removed :3
So the companion wouldn't have known!

Oh yes because robodogs, sentient AI, ghouls, supermutants and psychic powers are real down to earth.

So you've never been to Walmart?

Maybe not down to our Earth, smart@$$.
But all that stuff has at least been consistent with the previous Fallout titles.

Because if more than one person got teleported at the same time, the molecules would jumble up and we'd get 3 [censored] up Courier:ED-E:Veronica hybrids, and we all know if that had come to pass, the Mojave Wasteland would cease to exist.

Why can't companions come with you in any other Fallout 3 and New Vegas DLC barring Broken Steel?

So far the explanation has been that scripting errors and miscellaneous bugs would probably take place. And they'd rather not have to program in specific things for all companions every DLC.

I assume challenge is also one of the reasons.

Lol.
Some people just don't read.