Disclaimer: I'm not saying you can't/shouldn't use Discord for things that are actually convenient/useful to you. That isn't what I'm going for.
I've been getting increasing weird pressure to "JOIN THE DISCORD" in so many places in ways that are just an increase of background noise that I will never be able to keep up with but the norm seems to be to continue cranking up that background noise.
In a recent undisclosed PVP game that I otherwise enjoy, someone was spawncamping and griefing me (used to that, it happens in that game) and even that griefer kept messaging me to "JOIN THE DISCORD" with a link. Why would I want to join the Discord of someone that is actively griefing me? 
Even weirder, I asked that griefer that question, and they seem genuinely baffled about why that would stop me from "JOINING THE DISCORD."
I already make sure Discord is off by default and only turn it on when I'm actually using it to communicate with people for something like my tabletop games. Even then it's kind of annoying background noise and I don't like how intrusive and data-miney it gets.
Yeah I'm old and that makes my take on Discord solicitations invalid. Guilty as charged. 
This is like stopping cyber bulling 101 and kids need to understand that cutting off contact with an abuser is good.
Agreed, though I was genuinely surprised that the griefer was
in their response. No actual anger or even mocking or anything like that, just "why don't you want to join discord?" 
Makes me think it's probably a kid.
"Why don't you want to contribute to my candy-like craving for more artificial parasocial friendship accumulation, person I just griefed?"