One of the biggest reasons is probably the reason behind using any software as a service rather than doing it yourself: you can concentrate on what you do best and not spend time managing things yourself. A couple of our users switched from using open source alternatives for that reason. We've put a lot of time into our infrastructure and decoupling things so we're very resilient against outages so you don't have to. We've also put a lot of time into making our library more robust and well tested than any alternatives we've seen to date.
