But they're backed with thousands of programmers and designers

We are asked, "But they're backed with thousands of programmers and designers" Isn't this an advantage?

Although a platform has thousands of developers doesn't mean that they are all working to make the platform better. Many developers know how to build on the platform but most times look for plugins, apps to fill in the gaps in their business requirements. There are limited developers who work on the core platform. 

Once you customize a platform to meet a specific client requirement it then becomes a custom system that you need to continually pay to have upgraded.