Because you choose to? No One says you have to, unless maybe you are in an area that values the latest and greatest over proven results. Established programs

Because you choose to? No One says you have to, unless maybe you are in an area that values the latest and greatest over proven results. Established programs don't get re factored or rewritten in new technology all that much, especially big corporate systems. If you are freelancing or haven't worked on a long term project you probably are stuck in code du jour mode.