Why focus on some niche environment provided by a specific company according to their whims and needs when there is a vast body of languages, tools, libraries,

Why focus on some niche environment provided by a specific company according to their whims and needs when there is a vast body of languages, tools, libraries, and frameworks available in the free and open space? With the Internet dominating all applications are basically just stores of data with their related organization, logic, and interfaces. If you want to add a pretty face to such an app using languages, tools, libraries, and frameworks primarily developed and owned by a company you can do that with minimal risk as long as the core is outside that.