Sure thing. Mattermost and most open source chat tools not Google searchable. They can offer public communities but unless they are rendering static version of the site it is really not SEO friendly. They are very enterprise/security focused so if you want something secure and private Mattermost is fantastic.

We started out making Slack and Discord Google searchable and search engine friendly see: kotlin for example https://slack-chats.kotlinlang.org/ they have around 50,000 pages indexed by Google. We render a static version for Google while giving you the real time experience of a chat app.

Secondly most large communities end up being a community support channel. So for anyone with customer support experience having your conversation in one place is really crucial as well as some sort of open close state. I was also the author for https://github.com/papercups-io/papercups which made me a bit opinionated in terms of community/customer support

Finally most communities end up being too noisy and in part is because it is designed for chat. I actually don't think there is a great solution out there to manage conversations at a large scale and we think we can innovate on the UX of it.