Whoah.... no they absolutely weren't. Draconians were a replacement for orcs, and other 1E "bad guys to be killed". They weren't intended for players at all, and not until the book Draconian Measures and subsequently 3rd edition were they ever held up as a player race.
Half Dragons are not Dragonborn, and they appeared once in a niche 2E product (I love Council of Wyrms, and I own it, but its depiction of "half-dragons" does not match Krynnish half-dragons (who work completely differently, based on their very minor appearances in the lore).
In my current spelljammer game I banned Warlocks and Clerics as first levels options. Because (I don't think my players are on ENworld, so I can spoil it here) the campaign began with them waking up in an abandoned asteroid base in, what they later had figured out, clone tanks without memory of their past life.There are other reasons a DM might ban a class, rule, or spell, beside their whim or "setting integrity", or game balance."
For example, when I started running 5E, I outright banned warlocks. I had never played in or run a 5E game, but had read the PHB and had plenty of general D&D experience. Everyone else I was running the game for had even less experience with 5E or any edition of D&D. I bounced off the warlock and I didn't want to deal with learning a new class mechanic while a newb might also be trying to figure it out, while I also trying to satisfyingly integrate the idea of an otherworldly patron into the campaign narrative for the first time. So I told everyone to avoid it. (Though, I think if I had had a more experienced player (both with the game and with my DMing style) wanting to try it out for the first time, I would have likely taken that trip with them). Having had time to integrate them with the setting, and spend more time playing in game with them, my Vanity Frankenstein 5E, will include a modified version of the warlock tied more specifically into the setting..
Then again, the current homebrew setting I use bans* one of the game's core species (elves) as PCs, but they still exist in the game world! So my whim still rules supreme!
* though there is a potential elf-related replacement for elves and half-elves (the latter of which simply don't exist).
Why should they?
because it is the normal thing to do… when you ask me for directions and I give them in a way that is unclear to you, do you just head off not knowing where to go or do you ask for clarifications?
no they did not, they did not understand the parameters so they have no idea whether their ideas meet the requirements
no one is being forced to run anything, if the player shows up with an idea that does not meet the parameters, the DM will tell them and they will need to come up with a different idea then.
