Discord lacks many tools the community makes good use of and they're not about to change them so there were never big plans to switch to Discord.
Nobody uses it, and it's there, so that should say a few things, but for big communities TeamSpeak remains way ahead in terms of permission management, it's more solid and said permissions can be managed on the run, meaning people don't have to reconnect for them to be muted if the channel was modified for them not to have talk powers (works wonders in large meetings), aside from many other things, like the fact it doesn't need an account to join making it better for passersby, and that we don't have to purge inactive people every few months.
On top of it all, we don't rely on Discord servers being up or down, as TS servers are dedicated. << This point lately is especially important since the moment there are many people in a server Discord starts acting weird - Not to say their quality of service when it comes to server stability has been rather low lately, to the point where even Guilded, currently on Beta and with less funding has more stable servers.