IRC had a higher barrier to entry and a lot more common expectation of kickbans for various reasons (justified or not).

Plus the concept of +v doesn't really exist on discords. Sometimes you'd be stuck lurking while only a select few could speak.

And frankly being able to embed images/videos degrades the seriousness in various ways as it can become a bit of a meme/comedy competition (and they scroll disproportionately more text off.

And avatars mean less space is actually text..

<[@+]?shortnick>: <text>

is pretty much the optimal format for information density, which is ironic that twitch chat uses it (to mostly spam emotes)