Because people like to talk to each other sometimes.
And voice channels are a convenient feature people prefer rather than handling yet another tool with its own idiosyncrasies.
And voice is not enough, it also needs video and screen sharing. It all needs to be "free" (AKA someone else pay for it) too, or people will keep using Discord.
People should also be able to create their own servers without worrying about technical details, and again, without directly paying for it.
That's how high the bar is.
