Flexibility and familiarity. The Stratis Platform is designed to be as flexible as possible. Stratis Group Ltd were fortunate to be building out the Stratis Platform when they were: they were early enough to be the first fully C# Blockchain as a Service, but they were also able to learn lessons from previous BaaS offerings. The Stratis Platform is a very flexible, scalable platform for dApp and general blockchain development. The modular nature of the Full Nodes allow users to build their applications in whatever way suits their needs.
The Platform is built from the ground up in C#. You can read in more depth about why this is important here. Much of the corporate world uses the C# coding language and is familiar with the .NET ecosystem. If a business already has applications in the .NET environment, then it makes sense that they would wish for their application of the blockchain technology to exist within the same framework. No other BaaS offers this.