It's not just as easy as "if you don't like it, don't use it." Class bloat affects the game as a whole. Designers have limited amount of time and resources. Also, having too many classes limits the conceptual and thematic space of the other classes. Like how if sorcerer and warlock were one class, the resulting class could be mechanically and thematically less pigeonholed, it would have a greater number of subclasses when the designers wouldn't need to waste time writing duplicate subclasses for similar themes. I rather have fewer broader, more flexible and better supported classes, than loads of narrow, gimmicky and thematically thin classes.
Given the comparatively slow pace of published books in 5e, I sincerely doubt that design time is a factor in whether or not they add new classes. Hell, they even actively playtested several psionic class things before eventually scrapping the idea. I mean, do you feel that the books published during the months (was it years?) that they were working on the psionic stuff were dramatically worse than those from before? If not, that objection would seem to be far more theoretical than practical.
Absolutely disagree on the "limits the conceptual and thematic space of other classes." Why should it? Particularly if we're
adding new classes to what already exists? It's not like the addition of a Swordmage can
take away the Eldritch Knight, Echo Knight, Battlesmith, Hexblade/Blade Pact, Arcane Trickster, or
the entire Paladin class, after all. Making classes that share thematic elements is, if anything, par for the course, it's why people see similarities in the Druid and Ranger, the Cleric and Paladin, etc. The Cleric neither ceased to exist nor got sidelined because of the existence of the Paladin. They evolved in parallel to one another, both growing and changing as time went on. Again,
in practice, this concern seems to be largely inapplicable;
actual classes don't get trodden over just because there are thematic or conceptual similarities. (If anything, what
actually causes that trodden-over effect is people balking at classes being made too different!)
As for the Warlock and Sorcerer, I see it exactly the reverse. Both archetypes--Faust and classic Merlin--would be necessarily watered down, forced to both express the same fundamental tools. It would be ridiculous to merge the classes only to then make a whole mess of tangled exceptions for how you can't use X pact with Y patron or vice-versa. So you end up with "Pact of the Dragon" Sorcerers-as-Warlocks who, as noted, can apparently belch up a Book of Shadows because great-great-great-great grandma got busy with a bus-sized lizard. Instead of actually expressing those archetypes meaningfully, you'd be
taking away the ability to address that struggle with an innate part of yourself, or the struggle against imposed authority--and those are two very different struggles. Trying to pretend that "I
sold my soul to the devil" is the exactly the same as "I
am a devil inside" just makes both stories weaker.
Yes, I'm glad that there are not officially published options for the assassin's auto-kill and the swordmage class features that are so powerful and different that they can't be allowed to be used by anyone else. It's my opinion. I'm not doing anything to keep you from having them. I don't need them. I won't boycott WotC if they publish them.
Frankly, this sounds like arguing in bad faith; if you assume that the stuff that others want is broken, and
that's why you don't want it published, then you're assuming from the get-go that publishing them is bad. I, and others, have given easily half a dozen different potential approaches that do not in any way sound inherently broken and out of line with the rest of the game. So, since it apparently needs to be said:
assuming a Swordmage that is actually reasonably balanced, what harm does it cause to the table of Irlo and friends when published as an official document?
And frankly, most of such additional classes are not needed and are just bloat. The subclass system is great, people should utilise it more. With it you can have both broad and flexible classes and more specific themes represented via subclasses.
And there are some things where it simply doesn't work. People have told me--
repeatedly, and I want to say you're among them--that the kind of features Warlord fans desire are simply unacceptable as part of the Fighter kit. That alone indicates it needs its own class, if it can be implemented in a balanced way. Given the number of attempts to make it happen (including from Level Up, as I understand it), that certainly doesn't seem to be a wild notion.
You're also begging the question, as an aside. "Not needed and just bloat" is literally just repeating yourself, because all it means is "more classes bad, less classes good." "Bloat" is a pejorative to mock and insult any increase someone doesn't like. If you want to make an
argument out of it, you actually have to defend
why adding another class means things suddenly become "bloated," rather than just pointing the finger and shouting the insult.