Because you don’t need to have significant experience or rent a VPS in order to do that, and I can respect that. We don’t need to force FOSS developers to become proficient in everything.
What needs to happen is some kind of tool (ideally FOSS) that lets you spin up an actual forum with the same difficulty to set it up as Discord.
Actually, I wouldn’t be surprised if screenshots are disabled in that app considering the rest, to “stop leaking sensitive information”.