The biggest advantage of a dropout is that the differential can be removed for easy service on the bench. In addition vehicle dynamics that cause the housing to flex will not affect differential operation as much as they do with an integral carrier.
The biggest reason for the decline in removable carriers is the cost. Compared to an integral carrier type the removable carrier is more expensive to manufacture as well as being heavier than its equivalent.
If you have an OEM removable carrier there are options if you’d like to give it more strength or power, options like: