It's usually a good idea to lower friction and meet your users where they are. In the case of the React community, most have Discord accounts because Reactiflux was kicked off Slack for having too many non-commercial members. (Supporting open-source projects is an explicit non-goal for Slack.)

Discord welcomes open-source communities and is quite popular in the React community. If you are adding an open-source tool to the React ecosystem, those are both good reasons to prefer Discord. I certainly wouldn't want to build an open-source community on Slack after the way they handled Reactiflux.