Problem is that you are locking yourself. Even if this work for decades it can destroy your company. At some point, you will not be able to respond to change. More agile, faster-moving competitors will eat your lunch.

I am not suggesting rewriting to use new shiny things. If the platform is deprecated (32bit, mainframes, windows98, C89, etc) you migrate your code when it is still possible. Customers can still use an older version of your software is they are stuck in the past but you are not compromising future of your product.