They function differently, but in terms of what gets communities to actually form and stick around, I think they're very similar:

- Making a new space for your community is trivial for anyone; it can be done in seconds with a few clicks and all you have to do is choose a name.

- Many people already have an account, so you don't need to convince everyone to sign up for a new platform. (Which scales with the platform's size, like all network effects.)

- Communities have their own space they can adjust to their liking, rather than being a vague cluster of nodes with a similar interest like in other social networks.

- Owners of those spaces have a lot of leeway to run things as they see fit.

Personally, I don't like the growing trend of every community being a Discord server that is going to collect dust in the corner of my chat window unless I commit to keeping up with it every day, but I understand why it's happening. Discord is an adequate social hub for any project or hobby group with a very low barrier to entry, which is more important than the actual functionality being the best IMO.

I think that while Reddit's primary use is link aggregation, there's a secondary use for getting really niche questions answered by members of niche communities.For example, I have questions and answers on subs like r/powershell & r/xcode that still get replies years later because they solve a very specific problem.

A lot of communities are choosing Discord for their homebase location rather than Reddit, which really bums me out because I'm not a huge fan of public Discord servers and I miss seeing the posts from all the niche communities I'm in aggregated somewhere.

They might have once but every sub Reddit has at least one, “join my discord server” post a day it seems. People just want browser based BBS but weren’t alive when they were at their best.

Far easier to manage a focused community, disseminate information rapidly, maintain a history of information.

For example im currently playing though a mod pack for a game more that 20 years old; post about it on reddit and you get nothing; post on the discord and 30-40 active people will quickly get you the info you need.

Search reddit for info (using google because reddit search has never and will never work) You'll end up with post after post of [Deleted]. Its beyond useless.