One difference (so far as I know, I’m not an expert on either situation) is that MongoDB requires copyright assignment for contributions seemingly because the license is so restrictive they can’t offer their own service under its terms (without open-sourcing all the software they use to host it). So far as I know Sentry does not require this (although the restriction against running a competing service does not affect them since they are the service, so I’m not sure this argument really holds up that well). Also the fact that that one encumbrance is released after two years helps their case a lot in my eyes.