Because it is a better design choice
Not objectively so. This would have to be justified in terms of some design goal you
share with the publishers in order to actually be clearly a better choice.
For all the rest of these with "I think" and "I want", they are fine rationales for doing what you want at your own table. For rules used by millions, "I want" doesn't really cut it. Lots of people want lots of things.
Because I think D&D doesn't work when it is that customizable.
My table is working fine under Tasha's rules, thank you very much.
And I want a consistent experience of a core element like that from table to table.
If you want consistency of experience, watch Game of Thrones, or play Settlers of Catan. D&D is where we make our own, idiosyncratic stories and engage in individual creativity, not where we play for consistent experiences.
There is no significant value to me if my table is consistent with tables I don't play at.
At the moment, in the D&D game I run, there are no PCs of PHB races. I am playing in a Humblewood game, which has its own races - your games and mine are thus inconsistent, yes?
I like having a shared sense in a game of 'this is what dwarves are'
If "what dwarves are" breaks over ASIs, then what dwarves were was fragile to begin with. Poor, breakable dwarves!
Because making it customizable like that is going to make it that much harder for the GM to say "This is how these bonuses work in my game"
If the customizable case is what the players prefer broadly, I'm okay with that. Sorry.
Because it overcomplicates the racial portion of character creation
This is no more complicated than choosing which score goes into which stat, which players already do anyway.
I don't mind people home brewing or whatever, but if home brewing this is the default, it feels like it is just going to be a mess to me.
This isn't home brewing. This is shifting ASIs from being a definition of the race, to instead being definition of the individual PC.
People don't have to agree. But it isn't tryanny to like limits placed on this.
Okay. I accept it isn't tyranny. In suggesting it, you score at least slightly above violently despotic dictators. Bit of a low bar for acceptance, if you ask me...
Since I don't think anyone actually said it was tyranny, this seems to be refuting a point that nobody made, though.
I am sure there are parts of the game you also want to be consistent
Likely less than you think. I operate in an environment of diversity - when I switch tables, I am typically switching entire game systems. Changing these ASIs from one table to the next is trivial, by comparison.