Many managers have no concept of what goes into the design and development of a product. As a result, they consider their workers to be commodities, little more than interchangeable automatons. I know this from personal experience and I still have trouble understanding that kind of thinking.

I left a job due to a disagreement and I certainly did not expect that they would be too prideful to admit their mistake and make amends. I was a one-man development team and the company's financials literally relied on my software doing what it was supposed to do. They hired a mediocre programmer and charged him with replacing my software with Perl (my stuff was written in a custom language). I had an insider at the company who fed me information. After a year of trying, no progress whatsoever was made. I lost contact with my insider after that so I don't know what eventually happened. I figure that they had to discard everything and start over. Probably cost the company millions but their pride was worth more than the money.