It is a little more resource hungry than a lot of other forum software, and last I checked it didn't really support importing old posts etc across.
Part of the reason we have it is because @ampburner
is a huge nerd works in IT and thus is a regular at StackOverflow (this software is a spinoff project) and liked it for various conceptual reasons that are... not necessarily shared by a lot management groups. It also doesn't have some features that various people might consider essential.
Community Management does tend to get treated as a low priority by a lot of companies and often has to compete with Marketing for funding, so it can be hard for them to get nice things unless it's incorporated into a marketing campaign. At one point the official Hitman sites used to just link to Hitmanforum rather than have their own boards, so having forums at all is an upgrade from those days.
Hopefully a few companies will overcome these hurdles and realize the glory of Discourse soon.