[mcpherrinm]

Because you can save a quarter cent per unit by changing microcontroller vendors, but you have to use a new programming language for the new one?

Because you are involved in a lawsuit with the contractor that produced your previous version and using it would possibly be an admission it met requirements, even if your in-house developers had to completely rewrite it to make it safe?

Because new safety regulations mean you have to use a FIPS approved compiler and testing procedure?

Because it's a niche product and the only people in the world who know the problem domain work for you?