There are thousands, probably millions of small business critical pieces of code running on systems all over the world running more than just .NET code. You'll

There are thousands, probably millions of small business critical pieces of code running on systems all over the world running more than just .NET code. You'll have to emulate or recreate nearly the entire operating system, at which point... what did you accomplish? Businesses are going to compare the cost/benefits of upgrading their OS vs upgrading some old code, and decide it's not worth it. Perhaps you've been lucky enough to move to more modern systems, but you're in the tech circle. For everyone else, it's not an easy option. Have you ever worked for a fortune 500 company? There are systems that are nearly 20 years old with billions of dollars running through them. Moving that is not a light decision.