One big factor is being free from bundling proprietary, vendor-specific libraries that may also leak user's information or otherwise increase the security risk

One big factor is being free from bundling proprietary, vendor-specific libraries that may also leak user's information or otherwise increase the security risk footprint of your app. Having control over the services that make up the core of your business, as opposed to outsourcing and relying on 3rd-parties, can be very freeing and also cost effective in the long run.